In the world of high-definition TV, it doesn’t matter whether your budget—or living room—can accommodate Panasonic’s $70,000, 103-inch plasma screen or only something smaller and less expensive. Either way, you’ll face the same predicament you had before you went HD: nothing to watch.

The major networks are beginning to broadcast some prime-time shows in high definition, so fans of Desperate Housewives, The Office, and many other programs are in luck. But none of the networks broadcasts 24-7 in HD, and the vast majority of cable channels still lack HD counterparts.

But the landscape appears to be changing to keep pace with the rapidly growing population of HDTV owners. According to the Consumer Electronics Association, the number of HDTVs in the U.S. reached about 36 million by the end of 2006. (The country’s total viewing audience is 110 million.) Since 2001, three networks—Voom HD, Mojo, and HDNet—have begun broadcasting a total of 12 channels of original programming, each with a full slate of shows in high definition.

According to Bruce Leichtman of the Leichtman Research Group, a media consulting firm that issues an annual report about HDTV, these networks are trying to take advantage of an uncrowded field. “Although the networks are unknown brands, it’s still better to be one in 20 than one in 200,” he says.

Though recent data from the C.E.A. reveal that the average HDTV buyer is squarely middle-class and as likely to be a woman as a man, the three networks have primarily targeted the rich, young, and male—the technology’s earliest adopters.

Dallas Mavericks owner Mark Cuban—a youngish, rich male himself—launched the first of these networks, HDNet, in 2001. Its shows include Bikini Destinations, a travel show featuring scantily clad women in exotic parts of the world; Get Out! a show featuring scantily clad women in large cities around the world; and Geek to Freak, with former N.B.A. star Dennis Rodman. For the high-minded, there is Dan Rather Reports, a weekly newsmagazine that premiered last October. The network also airs a number of interview and concert shows.

“TV is all about great programming,” Cuban says via email. “However, great shows shot in HD, for HD viewers exclusively, take the TV experience to a different level. No other network was taking advantage of HD, so we created HDNet and HDNet Movies.”

According to Cuban, HDNet’s revenue is growing 8 to 10 percent monthly, and the network has more than 5 million subscribers. By comparison, premium cable channels Showtime and HBO have about 14.5 million and 30 million subscribers, respectively.

HDNet is carried by satellite services DirecTV and Dish Network, and cable operators including Adelphia and Time Warner.

The most comprehensive HD-only offerings come from Voom HD, which was originally conceived in 2003 by Cablevision as a satellite service to compete with DirecTV. After that venture failed in 2005, Voom was reborn as an all-HD network featuring 10 channels of original programming, each devoted to a niche such as travel, sports, arts, or gaming.

Voom’s shows make the most of HD’s potential to provide a nearly three-dimensional viewing experience. The GalleryHD channel, for example, features such programs as Artstar—an Apprentice for the art world—on which contestants compete for a solo show at a Soho gallery, and Art of the Heist, which chronicles some of the biggest art thefts in history. With HDTV’s higher resolution, paintings look remarkably vivid compared with how they appear on regular TV.

Voom is available only on Dish Network, which has 13.1 million subscribers.

The alpha male of high-def networks is Mojo. Aimed at men ages 25 to 49 who earn more than $100,000 a year, Mojo boasts stereotypical guy fare, such as three original shows focused on alcohol: Beer Nutz, about American beer culture; Three Sheets, which deals with foreign drinking customs; and Uncorked, an attempt to bring macho attitude to wine connoisseurship. Other shows include the reality series Wall Street Warriors, which follows traders and hedge fund managers, and I Bet You, a reality show about two poker players who bet on everything they come across (including women’s underwear). The network was launched in 2006 and is jointly owned by Comcast, Cox Communications, and a partnership between Time Warner Entertainment and Advance/Newhouse. (Portfolio.com is owned by Condé Nast, a member of the Advance/Newhouse group.) The network’s audience of 6 million is expected to increase after a major ad campaign for Mojo kicks off in May.

Though these networks target wealthy viewers, it turns out you don’t need a $100,000-plus salary to subscribe to them: Voom, for instance, costs only about $50 a month. The bigger hurdle is simply finding them. Persuading cable providers to carry any new network can be difficult.

“Mojo’s biggest benefit is that it’s owned by cable operators,” says Leichtman. Comcast, one of Mojo’s owners, is the nation’s largest cable operator, with more than 24 million subscribers. HDNet and Voom have higher mountains to climb as they try to make themselves available to more consumers.

Still, being out front in HDTV programming and creating a relationship with audiences is advantageous, says Philip Swann, president of TVPredictions.com, a site dedicated to providing information about new television technologies.

“As more and more people buy HDTVs, they’re going to turn to their friends and ask them, ‘What do you watch?’

The owners of HDNet, Voom, and Mojo are hoping you’ll respond with their network’s name.