Birthday Girl Britney's Big Night Out

By Mark Dagostino

12/03/2008 at 02:55 PM EST

After blowing out candles in London on Saturday, then a Tuesday morning celebration on Good Morning America, Britney Spears capped off her 27th birthday festivities with family and friends on Tuesday night.

But first, she helped NBC ring in the holiday season.

Spears (wearing a coat that covered her sexy party dress) taped a special greeting for the opening moments of Wednesday night's star-studded Christmas in Rockefeller Center 2008 (airing on NBC at 8 p.m. ET), then headed to the top of Rockefeller Center for a quiet dinner at The Rainbow Room with her father, Jamie, manager, Larry Rudolph, mom, Lynne, and sons Jayden, 2, and Preston, 3, a source tells PEOPLE.

Afterward, Spears ventured downtown for a combined birthday and album release party at the club Tenjune. Guests at the Big Top-themed bash – a nod to her new album, Circus – included Tyson Beckford, Jeremy Piven and Lance Bass.

One star who didn't make it in? Ugly Betty's Eric Mabius, who was turned away from the jam-packed club when he arrived with an entourage of friends.

Next up: Spears returns to L.A. where she will reportedly help light a 52-foot digital Christmas tree at the new L.A. Live entertainment complex Thursday night.