Celebrities like Donny Osmond and David Hasselhoff forgo the Hollywood high life for reality-show low jinks.

Seated in her trailer in the desert 35 minutes north of L.A., Kelly Preston is bad-mouthing a rival. ”I thought Donny Osmond would go down yesterday,” says the star of For Love of the Game. ”But Donny is different than what you’d expect—he’s very competitive…thinks he’s going to win it all.”

In bringing back its summer reality hit Fear Factor with a first-ever celebrity edition (airing Nov. 27), NBC has assembled the oddest collection of personalities since Gilligan and the Skipper set sail. In addition to Preston and Osmond, there’s ex-wrestler Joanie ”Chyna” Laurer, rapper Coolio, and Baywatch alums Brooke Burns and David Hasselhoff, all primed for sweeps humiliation. Imagine a 21st-century Circus of the Stars with fewer sequins and more adrenaline—and a $50,000 prize going to the winner’s fave charity (the others are guaranteed $25,000).

Six stars working together for good causes? Well, not exactly. Between standing on top of a moving bus and sticking their heads into a tank of live worms, the contestants are busy making sport of each other. Laurer loudly announces, ”Who’s the man!” Meanwhile, Coolio tells Hasselhoff that he’s going to lose because the competition isn’t shot in slow motion.

Fear Factor is like going to the ultimate amusement park,” says David Goldberg, president of Endemol USA, which produces the show. ”When other celebrities see it, they’re going to want to be on the next one.”

That all depends on whether stars are put off by the sight of Preston’s blond locks covered with critter excretions courtesy of superworms and their buddies, the giant millipedes. For participants, it’s quite a change of pace. ”Last week I was posing for Playboy in the most glamorous atmosphere you could possibly imagine, and this week I’ve got bugs all over my ass,” says Laurer. ”This is all foreign to me. I’ve never even been camping.”

No, Fear Factor isn’t your garden-variety celebrity game show. ”This is a lot harder to book than Weakest Link,” notes exec producer Matt Kunitz. ”There, you show up for eight hours, get abused by Anne [Robinson], and go home. You show up here for three days and you could actually get hurt. We don’t make the stunts easier just because they’re famous….This is Fear Factor, baby.”

And that’s fine with Preston. ”I’ll pretty much try anything once,” says the actress in her trailer between stunts—though she admits, ”being covered by the worms was pretty nasty.” She wants to send a message to Coolio, but it’ll have to wait until later. Her husband, John Travolta, has just arrived. He’s promised to match whatever amount she wins for the New York Police & Fire Widows’ & Children’s Benefit Fund—although he’s making no promises about actually leaving the cool confines of his black stretch limousine.

Back in his trailer, Osmond outlines his competitive strategy. ”I tell them I didn’t sleep much the night before so they think they have the edge,” he says, flashing his 500-watt choppers. ”When they’re talking smack at me, that’s what I love to hear. It builds the fire.” He laughs diabolically.

So who actually wins this competition? Host Joe Rogan remains tight-lipped, but he notes: “In Fear Factor, the smart ones don’t give predictions.” Will someone please tell Donny Osmond that?