PUSHING THE ENVELOPES
Britney Spears's Oct. 16 wedding invitations may be out-of-date, but they're more valuable than ever. The original 100 invites, which feature hand-beaded Chantilly lace and Swarovski crystals and are worth $300 each, have their own history. Designer Ellen Black of L.A.'s Lehr & Black, who worked closely with Spears to give the invites a "shabby-chic look," had mailed half of them to guests when she got a call saying the wedding would be a month earlier. "We had invitations that hadn't been sent, so we put a new piece [of paper] on top," Black says of the "Surprise!" invites handed to the 27 friends and relatives who arrived Sept. 18 for what they thought was an engagement party. But Black's earlier work continues to appreciate. "I've already seen one of my original invitations on eBay," she says. "Someone is trying to sell it for $4,000!"

OLSENS' WEEKEND OUTING
They broke up last month, but Mary-Kate Olsen and David Katzenberg still like each other. On Sept. 22, Olsen made a two-day trip to Beantown to visit the Boston U. senior. "They remain friends," says her rep. Olsen then headed back to New York City for the weekend, which she spent out on the town with sister Ashley. Wearing coordinating outfits, the 18-year-old twins enjoyed a sushi dinner, then hit the hot spot Bungalow 8. Restaurateur Scott Sartiano, 29, who has frequently been at Ashley's side since she moved to New York City, was along for the ride.

IT'S A LOCK
For those who have envied Jennifer Lopez's luxurious long hair at red-carpet events, take a second look. It may be a wig. According to a source close to the actress, "her real hair is shoulder length and thin. It's cute, but it's not movie-star hair, which has to be thick and beautiful." When she's shopping or working out, her real hair is usually pulled back into a bun, says the source, adding that it's easy to spot the wig. "The fake hair has a hairline that starts high up on her head because the wig sits on top of the real hair." A rep for Lopez didn't return calls.

MELANIE'S NEW GIG
Actors sometimes take pay cuts for projects they feel passionate about. In Melanie Griffith's case, she did it to be near Antonio Banderas while he's shooting the sequel to The Mask of Zorro in Mexico. "I'm on the payroll as a horse wrangler. I've been riding all my life," says Griffith. "I get $200 a week. It doesn't pay the bills, but it pays for my manicures. And most importantly, I get to be with my husband."

FAST TAKES
First twins Jenna and Barbara Bush had a rip-roaring good time at Chicago's nightclub Sound-Bar Sept. 23. Arriving just before midnight, they hit the dance floor and hung out with friends until 3:15 a.m.... Stella McCartney threw a party for Gwyneth Paltrow's 32nd birthday at her London boutique, adorned with balloons spelling the actress's name. The guests, including Chris Martin, noshed on cupcakes.... Lisa Kudrow was among the young moms at Mira Sorvino's baby shower at L.A.'s Chado Tea Room Sept. 25. Sorvino and husband Christopher Backus are expecting their first child later this year.