The ex Laguna Beach star turns 20 and celebrates with friends at Sideways

Kristin Cavallari helped kick off the grand opening of new Hollywood hot spot Sideways Restaurant & Lounge with an event of her own: a belated 20th-birthday celebration.

The dinner with about a dozen friends – including actor Nick Zano (What I Like About You), with whom she spent New Year’s Eve in Miami – started around 9:15 p.m. Thursday, the same night Britney Spears and her new beau Isaac Cohen also made an appearance at the new tapas joint.

“This is the first time I’ve seen my friends [in a while] so I’m having the best time,” Cavallari told PEOPLE. “I’m kind of getting over the club scene. I like this better because you can actually talk to someone instead of yelling at them. You can talk, eat food and just hang out with your friends.”

Just a week before that would’ve been impossible. The former Laguna Beach star ushered in her 20s by having her wisdom teeth removed Jan. 4, the day before her actual birthday.

Instead of partying, Cavallari “lied in bed and watched TV, which is actually nice because I haven’t done that in awhile,” she says, “but the whole wisdom teeth thing was a pain. Ugh. I’m just sort of able to smile again.”

Also seeming to put a smile on her face lately has been Zano. The two sat next to each other for most of the night. “He s a sweet guy,” she said. “I’m very happy now. I’m in a happy place.”

And she plans on keeping the positive vibe running through 2007. Her new year’s resolution? To “stop swearing,” Cavallari says. “I’ve made this resolution, like, five times and it hasn’t worked!”