Various-grade celebrities have already attempted dancing and skating on reality shows, and now a fresh slate of would-be winners will be mashing the gas for an ABC series set to air this summer. A dozen stars have signed on for the Fast Cars & Superstars - Gillette Young Guns Celebrity Race, with the would-be leadfoots including William "Take Her to Warp 7" Shatner, tennis champ Serena Williams and singer Jewel. This week, each celeb is behind the wheel for speed trials at Lowe's Motor Speedway in Charlotte, N.C., with top NASCAR drivers such as 2006 Nextel Cup champion Jimmie Johnson showing them the ropes.

In Monday's first practice sessions, as half the stars got trial runs in, a clearly rattled Serena Williams was at the bottom of the speed chart - with her best time slower than her vaunted tennis serve. NFL legend John Elway made a very respectable showing for a newcomer, with a bubbly Krista Allen hot on his heels.

The celebrity participants also include skateboarding legend Tony Hawk, seven-time world all-around rodeo champion Ty Murray, reigning WWE champ John Cena, surfer Laird Hamilton, volleyball queen Gabrielle Reece, Super Bowl-winning Steelers coach Bill Cowher and former NBA star John Salley ( The Best Damn Sports Show Period). The NASCAR "Young Guns" are Kurt Busch, Carl Edwards, Jimmie Johnson, Kasey Kahne, Jamie McMurray and Ryan Newman.

For more on ABC's Fast Cars, see TVGuide.com's Interviews & Features. - Reporting by Robert Edelstein