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Off the Dance Floor: Mills, 39, is an activist for the animal welfare group Viva! and the land-mine-clearing campaign Adopt-a-Minefield. Married to Paul McCartney for four years, the Londoner, who had her left leg partially amputated after being hit by a motorcycle in 1993, is now in a bitter divorce with him. They share custody of 3-year-old daughter Beatrice, who's become a great backup practice partner for Mills, who's teamed with Jonathan Roberts (right). "She loves to dress up in her princess dresses and dance around the room with me," says Mills.

Why She Signed Up: After a British tabloid falsely claimed she was on DWTS, Mills's publicist called up to offer congrats. "I said, 'No, I'm not! But how much fun would that be?'" After the rumor made it to the U.S., "ABC asked if I would do it," says Mills.

Biggest Challenge: The pain. "When you dance, you're twisting and twisting, so my leg burns [in the prosthetic]" says Mills, still adjusting to a new leg she had made for the show. "I had to drop my heel height—it's one thing walking down High Street in your four to five inches, but another when you're being thrown all over the place." Then there are the limitations of a prosthetic limb. "I can't do the heel and toe moves because I don't have a heel and toe that move, so I've got to fake it with my hips."

Why She Could Win: Voters will likely be impressed by her guts—and her sense of humor. "I've got a sleeve on the leg so it doesn't go flying off," says Mills, who did lose her prosthetic limb off a chairlift once. "It is funny!"

JOEY FATONE

Off the Dance Floor: The former member of 'N Sync, 30, also hit Broadway, first in Rent, then Little Shop of Horrors. He lives in Orlando with wife Kelly and daughter Brianna, 6.

Why He Signed Up: "I've been asked to do it every season. Now that I have the time, I was like, 'Okay, this looks like it's a lot of fun,'" says Fatone, whose partner is Kym Johnson.

Biggest Challenge: "Right now we're learning the quickstep. It's difficult because your feet are gliding and your upper body has to stay in the same position. It doesn't look beautiful right now. The balls of my feet are killing me a bit and my brain is a little jumbled."

What Fans Can Expect: "I want to have fun—and who doesn't want to win? We're going to bring a lot of entertaining stuff to the table. But if you want to see me in spandex, you have to vote me into the finals."

IAN ZIERING

Off the Dance Floor: Ziering, 42, is best known for his role on Beverly Hills, 90210, but he recently hit the film-festival circuit with a short he directed and produced. "Maybe I'll be a professional dancer next," he says.

Preparation: "I refocused my workouts," says Ziering, who's already lost 7 lbs. since he started practicing. "I've done a lot of flexibility training, balance and core work. I still go to the gym to do Pilates." The health-conscious actor also upped his calories. "For lunch, I used to just have a plate of egg whites, but now I have a white toast, peanut butter, banana and honey kicker!"

Biggest Challenge: "At a nightclub, your body just does whatever it does. With ballroom, the music has to stop in your head, you have to analyze it, then send the right movements to the different body parts! After three or four hundred times, it starts to sink in."

Why He Could Win: In past seasons, Ziering's partner Cheryl Burke helped both Drew Lachey and Emmitt Smith take first place. "She's phenomenal," says Ziering. "I'd like to see her be a three-time winner."

LEEZA GIBBONS

Off the Dance Floor: The former Entertainment Tonight cohost, 49, and mom of three has a radio show and runs a nonprofit for Alzheimer's patients and their caregivers.

Preparation: "I gathered up my life coach, my fitness people and my girlfriends and said, 'I'm freaking out and need your help!'"

Most Looking Forward To: "This year, no one's kicked off in the first two weeks, so I'm guaranteed to be dancing [with partner Tony Dovolani] on my 50th birthday [on March 26]!"

APOLO OHNO

Off the Dance Floor: The speedskater, 24, is an Olympic gold medalist and just won five more medals at the world championships in Milan.

Why He Signed Up: "It's an experience!" says Ohno, who initially didn't realize that the show (where he'll dance with Julianne Hough) aired live. "I said, 'So when I fall on my face, everyone will see?'"

Biggest Challenge: "I'm not in my element. I didn't consider this a sport, but I have respect for dancers now."

SHANDI FINNESSEY

Off the Dance Floor: 2004's Miss USA, 28, hosts Lingo and PlayMania on the Game Show Network.

Dance History: "I can do the robot, the running man and the macarena," says Finnessey, who's paired with newcomer Brian Fortuna.

Preparation: "I should have been going to the gym, but instead I was thinking, like, 'Last supper!' so I pigged out on all this junk food. I'm getting healthy again. Now McDonald's totally gives me the McCramps."

CLYDE DREXLER

Off the Dance Floor: The ex-NBA star, 44, now does home-game commentary for his former team the Houston Rockets.

Why He Signed Up: "I've always told my four kids not to be a wallflower."

Biggest Challenge: Being 6'7". Partner Elena Grinenko "is up to my chest, but you have to keep your head up, so I can't see anything," says Drexler.

Why He Could Win: The graceful giant's nickname on the court? "The Glide."

LAILA ALI

Off the Dance Floor: Ali, 29, is the reigning super-middleweight boxing champ. (She got the genes from dad Muhammad.)

Dance History: "When I was 8 or 9, I took tap. My dad wasn't a big dancer. He's like, 'Show me your moves!' He's excited."

Biggest Challenge: Costumes that stay on when partner Maksim Chmerkovskiy dips her. "I don't even like the word 'skimpy,'" says Ali. "I don't want my chest to look like it's going to fall out!"

BILLY RAY CYRUS

Off the Dance Floor: The "Achy Breaky Heart" singer, 45, stars with daughter Miley, 14, on the Disney Channel's Hannah Montana.

Why He Signed Up: He was scared until daughter Noah, 7, "came home and said, '[My teacher] said never let the fear of striking out keep you from playing the game,'" says Cyrus, who'll dance with Karina Smirnoff.

Biggest Challenge: "I'm not a dancer—I don't even know the Achy Breaky dance!"

PAULINA PORIZKOVA

Off The Dance Floor: The former model, 41, has a novel due in April.

Dance History: "I've never exercised in my life and now I'm dancing six hours a day. I'm in so much pain; the only things that don't hurt are my teeth and eyeballs. My poor husband [Ric Ocasek]. Every time he touches me, I'm like, 'Ow!'"

Biggest Challenge: Standing up straight. Partner Alec Mazo "is like, 'What's your problem with posture?' I'm like, 'Can't I elegantly slouch?'"

JOHN RATZENBERGER

Off the Dance Floor: The former Cheers star, 59, currently hosts John Ratzenberger's Made in America on the Travel Channel.

Why He Signed Up: He happily agreed to fill in when actor Vincent Pastore dropped out. "I said, 'Let's win this for the baby boomers.'" Now he's making up for lost time. "I applaud [partner Edyta Sliwinska's] work ethic—we're not here to have a tea party."

Why He Could Win: Fans are already lining up to give him tips. "They say, 'Okay, when you do the cha-cha...' right in the supermarket! It's really a wonderful thing."

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  • Contributors:
  • Reported by Monica Rizzo/Los Angeles,
  • Michelle Tan/Los Angeles.