Jim Clark, the Silicon Valley guru who helped found Netscape and made billions off the Internet's tear through Wall Street, has turned to a new darling of the investment world: Miami real estate.

Clark and longtime lieutenant Thomas ''TJ'' Jermoluk are poised to announce two condominium projects they want to build in Miami, including a pair of 55-story towers in the blighted area across from the AmericanAirlines Arena.

The complexes will be the first venture into real estate for the duo that made their fortunes during the 1990s technology boom, and then sold their companies for billions before the Internet stock bubble burst in early 2000. Now they are wading into a sector with its own bubble concerns, as industry watchers ponder how much longer the real estate market's five-year buying binge will last.

Jermoluk, the former chief executive of Internet portal Excite@Home who ran most of Clark's ventures, said Friday he has no doubts about his latest business model.

''I did a lot of diligence because I was new to the area,'' Jermoluk, 46, said in a telephone interview from his New York office. ``The conclusion I came to [was] the fundamental economics of the area are some of the best in the U.S.''

Clark and Jermoluk want to build in Miami's urban areas near Biscayne Bay, where land is cheaper but the views are still impressive.

Arquitectonica, a prominent Miami firm with an international reputation for unconventional architecture, designed the two projects: Blue, a curved 36-story building by the Julia Tuttle Causeway; and Mist, an imposing 55-story, 500-unit complex on Biscayne Boulevard in downtown Miami.

''Jim has sort of a legacy he'd like to leave,'' said Paul Murphy, the Miami builder working on the projects. ``He feels if he could deliver interesting architecture and sculptural architecture to the market, that's what he wants to do.''

Murphy is supervising the construction of Clark's new mansion in Palm Beach County, and said he has been pitching Clark and Jermoluk on real estate projects for about three years. They finally bit on the Blue property -- a close-quartered lot once slated for luxury rental apartments in a deal that stalled for lack of funding.

Capital isn't much of a problem for Clark. AOL bought the Netscape web browser system for about $10 billion in stock four years ago -- a deal that's since diminished with AOL's stock slide, but which still made Clark one of Internet's biggest winners. Before Netscape, he and Jermoluk ran Silicon Graphics, an early technology-sector success that has since seen its fortunes ebb.

''I think his business sense and timing was impeccable, as was his getting out at the top,'' media analyst David Joyce, of Coral Gables' Guzman & Co., said of Clark. ``You didn't hear too much from him afterwards. He realized lightning struck at least twice.''

Jermoluk described Clark as a silent partner in their real estate company, named Hyperion Development Group. Clark was traveling in Bali and unavailable for comment, according to Hyperion's public relations agency, but Jermoluk is settling into his new condominium at South Beach's Il Villaggio.

A partner at a New York venture capital fund, Jermoluk said his post-Internet days has left him with considerable time on his hands, so he was looking for a new project. South Florida real estate appealed, he said, because of the region's engine of new buyers: people from the Northeast and Europe looking to vacation, and Latin American buyers eager for investment havens.

Jermoluk, chief executive of Hyperion, has an ambitious schedule for company: five condominium projects under way at any one time.

''I've always believed go bigger, or go home,'' Jermoluk said. ``We decied we were really going to try and make this a big deal.''

The Biscayne Boulevard corridor is in the midst of a building boom, with developers targeting much of the scruffy waterfront for high-rise residential projects. Jermoluk and Murphy said they hope to attract professionals who can afford to buy in the middle of the market, with Blue and Mist's units selling for about $400,000.

Blue won city approval and would open in two years; the developers submitted plans for Mist to the city on Friday.

Mist would be the first condominium project built near the arena. City officials have pressed for residential development there, but so far no one has tested the market. The One Miami condominium tower is under way several blocks south in Miami's office district, but at lower prices than what Hyperion has proposed.

''In my opinion, that's on the high end,'' said Lewis M. Goodkin, a real estate consultant with PriceWaterhouseCoopers, said of the $400,000 price points for both projects. ``That area is still really not established.''

Jermoluk said he and Clark actually kept their prices low to lure buyers, noting both projects will each be a single-unit wide in order to give them a sleek, minimalist look.

''That's not the most efficient way to build a building. But it's the more beautiful building,'' he said. ``One of the nice advantages Jim and I have is we've already made money, in a different field.''