Christina's Sexy Halloween

Christina Aguilera and fiancé Jordan Bratman play doctor at the singer's Halloween party at Nobu in the Hard Rock Hotel amp Casino in Las Vegas on Saturday. (The pair have yet to tie the knot, but Aguilera's nametag already reads "Nurse B.")

No, Paris Hilton – in sexy cavewoman mode – isn't being arrested for overexposure. That's her sister Nicky (left) masquerading as a cop as the costumed hotel heiresses head out to a Halloween party in Los Angeles on Friday.

Ashley Olsen shows her own interpretation of dressing up for Halloween: The actress-NYU student trades her typical boho-chic duds for a couture gown at Fendi's All Hallow's Eve party in New York City on Saturday.

Desperate Housewives star Eva Longoria – decked out in an Alex Perry dress with matching Jane Lambert headpiece – is sitting pretty on the sidelines during Derby Day at the Melbourne Races in Australia on Saturday. The actress was on a plane from Down Under less than 24 hours later, heading back to Los Angeles to film a new episode of her ABC show.

Jennifer Aniston and Clive Owen seem to be on the right track at the New York City premiere Sunday of their movie, Derailed. "This is a sexy, psychological thriller," Aniston said of the film, in which she and Owen play lovers who meet on a commuter train.

Denise Richards snuggles with daughter Sam, 20 months, while dining al fresco Saturday in Malibu. Also at the lunch: Richards's daughter Lola, 5 months, Melissa Etheridge and Etheridge's partner, Tammy Lynn Michaels.

Ben Affleck keeps a tight grip on wife Jennifer Garner on their way to Starbucks near their Brentwood, Calif., home Saturday. Garner, who is expecting a girl in November, attended a baby shower a week earlier.

Reese Witherspoon is just an everyday mom as she crosses a Santa Monica street with 2-year-old son Deacon on Thursday. But Nov. 18 she'll be back on the big screen in Walk the Line.

Halle Berry stays in step with her main man, her Their Eyes Were Watching God costar Michael Ealy, after having breakfast in Hollywood on Wednesday.

Jennifer Aniston keeps a low profile on her way to the restaurant Babbo in New York City on Thursday. The actress is in town promoting her new thriller, Derailed.

He's not the King of the World, but Prince William will at least make a fine leader on the field. The heir to the British throne, who joined a training session at a London football field Friday, is the newly designated president of the English Football Association.

Sandra Bullock and Meryl Streep, both in Valentino, attend the

Fashion Group International's 22nd annual Night of Stars at Cipriani's New York on Thursday. The two actresses were almost costars: Bullock dropped out of Streep's film Prime (she was replaced by Uma Thurman).

Madonna leaves a London exercise class Friday. The singer's other extracurricular activity: trekking around the world to promote her album, Confessions on a Dance Floor.

Donald Trump and wife Melania Knauss make a pair of well-heeled parents-to-be at The Fashion Group International's Night of Stars party in New York City on Thursday. Knauss is expecting the couple's first child this spring.