MURRELLS INLET, S.C. — Ettore and Larisa Costanzo are showing off their new house, which they love madly.

“Notice how we upgraded so there’s tile on all the floors,” said Mr. Costanzo, a retiree from Brooklyn. He pointed to the Kashmir granite in the kitchen. “It’s nice, no?”

Now if only they could get the keys and go inside, instead of peering in the windows like a couple of Peeping Toms.

The house, on which the couple made a down payment of $88,820, is empty. Their belongings are in storage. They live, unhappily, in a hotel.

“It’s very upsetting, not to be allowed in our own house,” said Ms. Costanzo, a Russian immigrant. “Please take our money and let us move in.”

Their builder is Levitt & Sons, a unit of the Levitt Corporation, which ran out of cash in October and declared bankruptcy in November. All work on this planned 460-home development for retirees, grandly named Seasons at Prince Creek West, has ceased. The Levitt employees were laid off, the subcontractors put down their tools, and the Costanzos found themselves in limbo.

The collapse of Levitt, the first big home builder to fail in the current slump, illustrates how the turmoil in real estate is spreading far beyond subprime borrowers who cannot pay their mortgages. Levitt had a fabled brand, decades of experience and enthusiastic customers with good credit, but none of that was enough to save it.

Paul S. Singerman, Levitt’s bankruptcy lawyer, said that as the real estate market in Florida went into “an absolutely unprecedented and catastrophic downturn,” the builder’s customers across the Southeast became victims. “There is a bad story, an unfortunate story, about every customer that placed a deposit,” Mr. Singerman said.

Seasons is less than a quarter finished. About 90 buyers have paid a total of $3.48 million in deposits for houses in varying stages of completion, ranging from all but done, like the Costanzos’, to unadorned dirt.

Another 90 houses are occupied, but many of these residents are, if anything, even more unhappy than the depositors. Levitt sold them on a community where everything would be taken care of. Those assurances mean little now.

“I can’t believe we’re dealing with Levitt & Sons,” said Nancy Harth, 59, who moved in last March. “It feels like a start-up company.”

The initial popularity of Levitt’s 18 retirement communities — at least 4 of them are now in as much disarray as Seasons — is testament above all to the durability of a name.

Sixty-one years ago, Levitt began mass-producing homes on a patch of Long Island potato fields. It quickly built tens of thousands of houses in Long Island, New Jersey and Pennsylvania, creating the modern suburb in the process.

In recent years, the builder has been concentrating on projects for the children of the Levittown generation, the 78 million aging baby boomers. Its sales strategy leaned heavily on both the company’s long operating history and its long-ago achievements.

The pitch worked brilliantly.

Christine Roberts was born in Queens in 1966. Six months later, her parents moved to Levittown, and Ms. Roberts lived there for 38 years. “Buying at Seasons meant I was still going to be part of a Levitt community,” she said. “We thought that was so cool.”

She and her husband, Richard , like the Costanzos, are now full of uncertainty. They sold their Long Island home a year ago in preparation for their move to Seasons, and spent $10,000 on new furniture. With their Seasons house unfinished, they have been living in a trailer they own in the Poconos. Their furniture is in storage in South Carolina.

“We didn’t think anything bad was going to happen,” said Ms. Roberts, a former worker with the United States Postal Service. “We really and truly had the utmost faith.”

Many of the Seasons buyers came from the New York area. South Carolina offered a milder climate, lower taxes, less congestion and more golf. The development is about five miles south of Myrtle Beach, S.C.

“We raised our children. We’ve done the grandchildren thing,” said Karin Beaupre, who taught elementary school in Lynn, Mass., for 30 years. “It was time for us. So we took all we had and put it into this.”

Nancy Darr, 61, has macular degeneration, an eye condition that prevents her from driving and makes her unable to distinguish between a flower and a weed. She wanted a house, but couldn’t do the upkeep.

Seasons promised to take care of her concerns. The gated community would have 24-hour security. An activities director would arrange entertainment. Owners would not have to mow their lawns. Even their bushes were to be fed by a central irrigation system.

Best of all was the promise of a clubhouse.

The 29,000-square-foot recreation center would have tennis and bocce courts, a fitness center, and indoor and outdoor pools. There was to be a ballroom with a stage, a room for card games and another for billiards. Levitt promoted it as “a luxury cruise ship on land.”

“If you wanted to socialize, you could walk over and just mingle,” Ms. Darr said.

Everyone had plans for the clubhouse. Ms. Darr wanted to swim and work out. Andy and Pat Hudak were looking forward to dancing the jitterbug, as they used to.

“We didn’t buy a house; we bought a lifestyle,” said Mr. Hudak, 68, who ran a messenger service in New Jersey. They signed a contract in March 2006, paying $58,508 for a deposit and upgrades.

Selling a lifestyle was something Levitt perfected long ago.

Thanks to the builder, Time magazine noted approvingly in a 1950 cover story, buying a house was suddenly easier than buying a car. The original cost was $6,990, about $70,000 in today’s dollars; government-backed mortgages and low down payments smoothed the way. A second Levittown rose in Pennsylvania and a third in New Jersey (now called Willingboro).

William J. Levitt, son of the company founder and chief engine of its success, took the company public in 1960. It was acquired by International Telephone & Telegraph in 1968, and then sold in a court-ordered divestiture three years later. The company went through a succession of owners, relocating to Florida in 1979 and declining into insignificance.

In 1999, BankAtlantic Bancorp purchased Levitt. Under the leadership of BankAtlantic’s chief executive, Alan B. Levan, the builder began acquiring large chunks of land, first in Florida and then in neighboring states. The Levitt Corporation became a public company in 2004.

The product changed in a half-century, of course. The houses at Seasons are not the tiny boxes of the original Levittown but expansive dwellings with whirlpool tubs and marble vanity tops. With upgrades, prices reached $450,000.

But they were still sold as Levitt houses. Home movies of early Levittown residents dancing on their lawns played in the sales center and on the Web site. A pamphlet giving a detailed history of Levitt’s glory years was passed out to prospective buyers.

Nancy Darr, who had once watched her condominium developer go bankrupt, asked her Levitt salesman whether the company could fail.

“This is Levitt & Sons, America’s oldest home builder. We built Levittown,” Ms. Darr remembers him replying. “It’s a solid company. It’s listed on the stock exchange. This could never happen.”

Gary Drejza, a former Seasons salesman, confirmed that such assertions were routine. “We felt they were the truth,” Mr. Drejza said. “We believed.”

He must have, because he bought a house himself. “Want to see it?” he asked, pointing from the window of his Mercedes-Benz at Lot 49, still a pile of dirt.

Mr. Drejza now has a somewhat different view. “A name was purchased, that’s all. There’s really no remnant of the old Levitt. None of the family,” he said.

That might be no guarantee of satisfaction either. William J. Levitt, trying to make a comeback in Florida in the late 1970s and early 1980s, was forced to refund thousands of deposits when he failed to build the homes.

Booms are great, until the hangover. Mr. Drejza’s conclusion is that Levitt got “caught up in the madness,” buying too much land for too many new developments for too much money.

Analysts echo that view. “They tried a national expansion at the very worst time,” said Eric Landry, an analyst at Morningstar, the investment research firm.

In the bankruptcy, the Levitt Corporation is trying to sever itself from its Levitt & Sons division. Only the latter is insolvent. Mr. Levan, the chief executive of the Levitt Corporation and BankAtlantic, declined through a spokesman to be interviewed. BankAtlantic is based in Fort Lauderdale, Fla.

Seasons residents express confidence that another developer will finish the neighborhood, including the clubhouse. But privately, many acknowledge a lot of misery. “By the time the clubhouse is up,” said Jim Blake, 70. “I don’t even know if I’ll be alive.”

Damon Savino, who drove a truck for a lumber yard, feels particularly bad. He praised Seasons to his pals. Five of them bought houses; three are unfinished. “I’m losing friends here,” he said.

At a court hearing in Fort Lauderdale just before Christmas, Wachovia Bank, which is Levitt’s largest creditor, agreed to provide $10 million to finish at least 80 homes in Georgia, Florida and South Carolina.

The Costanzos, the buyers with the all-tile floors and the granite countertop, are optimistic. “We’re going to get our house,” said Mr. Costanzo, 64, a former shoe salesman for Salvatore Ferragamo.

Few of the other depositors seem as relieved. Sixteen of them held a conference call after the hearing. Fifteen said they did not want their house at the contracted price unless the clubhouse is built.

Mr. Singerman, Levitt’s bankruptcy lawyer, said he did not think that was likely anytime soon. Wachovia declined to comment.

Dave Whalen, a retired analyst with the New York City Transit Authority, does not have even the illusion of a choice about building or walking away. He put down $46,635 for a house that was never started by Levitt. That means Wachovia is unlikely to bother with it.

“We end with nothing,” said Mr. Whalen, 62. “I might as well have taken my deposit, put it in $1 bills, and let them blow off the front porch.”

Jim Clark and Tom Jermoluk cut a swath through Silicon Valley in the 1990s with companies like Silicon Graphics, Netscape and WebMD. But they are finding that it is a lot harder to maneuver through the real estate market than to master the Internet.

Five years after they decided to put their entrepreneurial talents and technology fortunes to work building Miami condominiums, the first two projects by their company, Hyperion Development, are plagued with delays and unhappy buyers. Some residents at the first tower, named Blue, are threatening to sue the company for not delivering on amenities, while other owners at the 330-unit complex are trying to sell their condos for less than they paid.

Blue’s problems have hurt Hyperion’s reputation so much that consultants say some buyers who put down deposits at the company’s second tower, the 516-unit Marina Blue, may decide not to close. Other Marina Blue buyers have sued to get their deposits back.

The problems raise questions about the ability of Hyperion to repay a $110 million construction loan as well as its ability to develop future projects in the Miami market. They also offer a look at what can happen when entrepreneurs try to trade on their reputation as they branch into other areas.

The setbacks are an unexpected turn for the two partners chronicled in the book “The New New Thing” by Michael Lewis as having a magic touch at starting multibillion-dollar technology companies. They entered real estate with plans to build four or five projects in Miami and named their company after Mr. Clark’s 155-foot yacht, Hyperion. His net worth has been estimated at $1.4 billion.

Mr. Clark, 63, and Mr. Jermoluk, 51, are not the only successful entrepreneurs who are struggling in Miami real estate. Builders throughout the area are facing rising construction costs and a slowdown in demand. Many buyers who paid deposits at the height of the market a couple of years ago now own apartments that are worth much less than they had agreed to pay. Many are trying to sell.

Another developer, Joe Cayre, who amassed a fortune distributing videotapes to Wal-Mart and who became a financial backer for the redevelopment of the World Trade Center site, faces lawsuits and delays on his 54-acre midtown Miami project. Even Jorge M. Pérez, head of the Related Group, who is on the Forbes list of billionaires with Mr. Clark, has retreated in the face of lawsuits and losses.

“It doesn’t matter who the developer is, where the project is located, what price range the units are,” said Jack McCabe, a real estate consultant in Deerfield Beach, Fla., who has tracked Marina Blue for hedge funds seeking distressed properties. “Every project is going to take hits, some more than others. None are insulated, and it doesn’t matter whose name is associated with it.”

In an e-mail message, Mr. Jermoluk compared today’s real estate market with the boom and bust in technology during the last decade. He likened the construction challenges — weather, worldwide concrete and steel price increases — to “memory chip shortages and price increases.”

“Anytime you start a new company in a new business,” he wrote, “you learn things.”

The slowdown, Mr. McCabe said, has developers in Miami trying to sell 52 multifamily sites that they once marketed as condos. Three other sites, he said, have fallen into foreclosure.

At Hyperion, the name Jim Clark was what attracted many prospective buyers. In 2003, Hyperion started its Blue condo project with a cocktail party where guests mingled with models painted head to toe in blue while partaking of the “usual finger food and free-flowing Champagne,” said Elaine Silverstein, a Miami advertising executive who attended the party.

She said that many guests had been interested in meeting the pair from Silicon Valley with a “marvelous reputation.”

“They were there to take advantage of this moment in time,” Ms. Silverstein said. “They were businessmen.”

Mitesh Gandhi, an information technology consultant in North Brunswick, N.J., remembers spotting Mr. Clark’s photograph and mention of his link to Netscape when he walked into the Blue sales office in early 2005. He and his wife paid a deposit for a $555,000 condo.

But they were disappointed when the apartment was finished — they did not like the lobby and did not feel safe in the neighborhood. They also said they thought the building needed more amenities.

“When we closed on the unit and walked through the lobby, we were like ‘O.K., this looks kind of bland,’” he said. “There’s nothing for me to do but try and sell it.”

The couple has priced the condo at $56,000 less than they paid. They have competition.

Their broker, Samir Patel, said 88 condos are for sale in the 330-unit building at prices ranging from $300,000 to $1.25 million. Blue’s condo president, Sharon Walker, said the board has hired a lawyer to help resolve construction defects and other questions.

Ms. Walker said Hyperion did not deliver the spa, restaurant and lounge it promised, not to mention falling short on “the quality and the workmanship and the four or five stars that we were buying.” While the complaints may seem minor, residents say they bought with a certain expectation of what the homes would look like.

“We have a lot of empty space in here,” Ms. Walker said, “that was supposed to — as I understood — have the lounges and the media rooms and all of the bells and whistles.”

Mr. McCabe, the real estate consultant, estimates that nearly 130 buyers at the 516-unit Marina Blue may not close on their condos. Another dozen have sued to get out of their contracts, he said, and buyers who put down deposits are trying to sell 250 more units.

Mr. Jermoluk disputes that there are problems. In an e-mail message, he said that he expected all Marina Blue buyers to close and that Hyperion was meeting its obligations even though construction costs had increased 30 percent because of rising steel and concrete prices.

He did not respond to a question about what might happen to the other projects they had planned.

Bernd Schmitt, director of the center for global brand leadership at Columbia University Business School, said Mr. Clark’s problems in real estate should not be surprising.

“You could ask the question whether it was a wise thing for him to use his name, which is very much associated with Netscape and the tech industry, to a real estate venture,” Mr. Schmitt said. “That was stretching the brand quite far.”

Other wealthy entrepreneurs seem to have found themselves in unfamiliar territory as well. In 2002, Mr. Cayre, the videotape distributor, and fellow investors bought the 56-acre former Buena Vista Rail Yard to build offices, shops, a hotel and condos.

Today, his company, Midtown Equities, faces roughly three dozen state and federal lawsuits over the project, mainly from buyers who want their deposits back for buildings that were delayed or never started. Mr. Cayre told a reporter for South Florida CEO, a regional business magazine, that he did not expect to make money on his first condo tower, Midtown Two.

But Stuart Weiss, a consultant representing private equity firms buying troubled projects, said that Mr. Cayre was at risk of losing even more money because of the neighborhood. “This is a real secondary location any way you cut it,” he said.

In an e-mail message, Mr. Cayre said he remained confident that his project would emerge as one of Miami’s best neighborhoods.

The market changes have forced a third developer, Mr. Pérez, who has built 50,000 condos in Miami over the last decade with Related Group, into a defensive position. Now he is battling a lawsuit from buyers of 38 apartments at Harbour House and 26 condos at Biscayne Bay.

His company is operating in emergency mode. He has set up a team to raise capital to buy back apartments that he expects buyers will not close on, and he is focusing on two kinds of condos: $4 million apartments for the high end, and urban housing that costs $200,000 to $300,000 a unit.

There are some things, he said, that even billionaires cannot control.

“We are just in the down part of the cycle,” Mr. Pérez said. “You can’t exclude yourself from the market.”