She doesn't want to talk about her hair.  Maybe that's why Jennifer Aniston, the 27-year-old star of the NBC sitcom Friends, bared her behind on the cover of Rolling Stone last March: She was so sick of being known as the cut to clone, she just wanted to change the subject.  So now the subject is her butt.

  "The first dress I tried to put on for the Marie Claire cover shoot wouldn't fit over my hips," she says.  "I was laughing, and then I said, 'Could we hold the rest of the dresses up to me first, so I don't have to go through this?"  Jennifer's mortification was fleeing, however.  She seems pretty happy with the body that emerged a couple of years ago when she took her agent's advice and dropped 30 pounds.

  "I went to a nutritionist," remembers the Manhattan native, who moved to L.A. a year after graduating from New York's High School of Performing Arts.  "She nearly threw me out of her office.  I was eating mayonnaise sandwiches, fried foods, burgers.  So I started to eat healthy and work out.  I mean, I had never done anything," says the woman who was just named one of Hollywood's hottest bodies by In Style magazine.

  Meanwhile, Aniston was staying alive in the business, landing parts in short-running TV series.  Then, two years ago, she landed the part of Rachel, the rich girl turned waitress, on the sitcom phenomenon Friends.  Big-screen roles quickly followed: Three of her movies are due out this year, including this summer's She's the One, the second film from The Brothers McMullen writer/director/star Ed Burns.

  "No, I've never been cheated on," reports Jennifer, who plays a woman whose husband takes Cameron Diaz as a mistress, "but it's one of my biggest fears - being cheated on or left.  I guess that comes from watching my mom deal with it.  Aniston's parents, Days of Our Lives soap star John, and model-turned-photographer Nancy, broke up when she was 9.

  >Today Aniston is particularly close to her only sibling, older half-brother Johnny Melick, despite his early penchant for frightening her.  "Once, when we were young, he made me watch Friday the 13th, after which I went into the bathroom.  He'd snuck in there first and hid behind the shower curtain, then jumped out, wearing this horrible mask that had eyeballs falling out and snakes for hair.  I let out a scream and....Well, let's just say it was a good thing I was sitting on the toilet."

  Today, family and pals keep Aniston from freaking in the face of her megasuccess, as does "a boyfriend who's heaven."  That celestial honey is Tate Donovan, costar of the cancelled Fox sitcom Partners, whom she's been seeing since October and who recently took her to visit his family in New Jersey.

  "His parents are still together, he's one of six kids, and they were all really happy to see him," recalls Aniston.  "We sat around a big table in the house he grew up in.  I envy that so much."  She sort of moans at the sweetness of it all.  "I don't go for the big planned-out romantic gesture," the actress says, "but when he showed me his old bedroom, it was pretty romantic."