(FORTUNE Magazine) – When Mark Cuban's new reality show, The Benefactor, airs on ABC Sept. 13, it will be the second television program to star a billionaire businessman. The first, of course, is The Apprentice, featuring Donald Trump.

Like Trump, Cuban--who first rose to fame when he sold Broadcast.com to Yahoo in 1999 for $5.7 billion, and who is now the owner of the Dallas Mavericks--has a big personality, a big bank account, and a big mouth. Signs that the red carpet was getting crowded started to surface last month when the two began trading barbs in the press:

"I just want him to do better with the show than he's done with the Dallas Mavericks," Trump said to an audience of TV critics.

"I wish Donald nothing but the best on The Apprentice 2, and I hope it does as well as his casinos," Cuban responded.

The irony is that, TV shows aside, neither man is living up to mogul status. Trump's Atlantic City casino chain recently filed for Chapter 11 bankruptcy, and though Cuban's recent bets--on HDNet and 2929 Entertainment--have been big, they have yet to show signs of paying off.

Not that the free-spending Cuban is terribly concerned with money at the moment. (In addition to the Mavs, he also owns a 24,000-square-foot house in Dallas, homes in New York, Los Angeles, and Miami, and a Gulfstream V jet, which he bought online.)

"I'm really into experiences right now," Cuban said, when FORTUNE caught up with him in his Bunker Suite at the American Airlines Center in Dallas. He was wearing a gray T-shirt, jeans, and laceless running shoes with no socks. His desk featured a bobblehead doll--of himself. Cuban, 45, explained that in the past year he has become a father, has played basketball with the Harlem Globetrotters, and was put in a sleeper hold by Randy Orton at a WWE event. ("This big, huge, 6-foot 5-inch guy in a Speedo came up behind me and put a choke hold on me," he said. "It was great!")

After producing the WWE belt he received in the exchange, he sat back on a leather couch, put his feet up on a table, and started talking business. These days Cuban's main job is HDNet, the all-high-definition TV channel he has reportedly put more than $100 million into since launching it in 2000. The channel, the first of its kind, airs on the DirecTV and Dish satellite networks and all the major cable systems except Comcast, Cox, and Cablevision. But now that other prominent providers are adding hi-def channels--like HBO, ESPN, and Discovery--HDNet's prospects are much less clear. "I think whether it was a visionary step or an extremely expensive and poorly judged move remains to be seen," says Aditya Kishore, an analyst at the Yankee Group. Cuban says the channel could be profitable in five years.

The problem is programming. HDNet has yet to find its niche: It airs 24 hours a day and runs everything from concerts to Trans-Am car racing to Bikini Destinations: Acapulco. To provide content, Cuban launched another big idea: 2929 Entertainment. That company is now home to HDNet, two production companies, a distribution label, a video library, and the recently acquired 200-screen Landmark Theater chain. Cuban and his partner since Broadcast.com, Todd Wagner, want to be the first entertainment company to release movies--some that are produced in-house as well as acquisitions--simultaneously in multiple mediums: on HDNet, on Landmark's 200 screens, and on DVD. It's yet another genre-bending idea in an entrenched industry, but the details--such as plans for the DVD distribution--are still vague and far-off.

Of course, if you're short on content, one solution is to star in your own show. Just then, the promo for The Benefactor appeared on all five flat-panel high-definition TV screens at once. "Here we go," Cuban said.

The premise of the show is that 16 people compete to prove to Cuban that they have what it takes "to be successful." There were some goofy stunts and a shot of Cuban doing a breakdance spin on his back and bumping into a table. In the final shot, Cuban stands over a group of 9-year-olds and says, "And then, I'm going to come back next week and choose one of you to run one of my companies." It's a joke--and another shot at The Apprentice, in which Trump hires one lucky contestant to work for him. Cuban is simply giving away a million dollars.

As talk turned back to Trump, Cuban mentioned that the two men had run into each other recently at the American Century Championship in Lake Tahoe, Nev. Cuban's Fallen Patriot Fund was serving as the beneficiary to the celebrity golf tournament in which Trump was playing. In the name of publicity and experience, Cuban offered Trump a chance to purchase his services as a caddy. The money--a pricetag of $25,000 was thrown around--would go to charity. After thinking it over, Trump declined.

--Grainger David