Pregnant Moment in the Libby TrialScooter Libby's defense team received a last-minute boost from a new addition to the crew yesterday: Frances Somerville O'Brien, 7 pounds 9 ounces. Alexandra Walsh, part of Libby's legal posse, headed to the hospital yesterday with her husband Brendan O'Brien, The Post's Carol Leonnig reports. Walsh was experiencing contractions a day after she was due to give birth, but hospital workers told her it wasn't time and sent her home.

The couple stopped at O'Brien's mother's house on the way back from the hospital and the contractions started all over again. Walsh realized she was too far along -- and O'Brien delivered his new daughter. At his mother's house.

Walsh is "feeling great and happy," Libby lawyer K.C. Maxwelltold us yesterday. "She's Supermom." Baby Frances is the family's third child, after a 5-year-old and a 20-month-old.

Maxwell said the members of Team Libby planned to visit the new baby at George Washington University Hospital yesterday (once court adjourned, of course).

Don't expect Walsh, one of Washingtonian magazine's 2006 "40 Top Lawyers Under 40," to go off the case: She was already e-mailing about work matters a little more than an hour after giving birth.

Kennedy: 75 and Doing FineHere's hoping Ted Kennedyis ready to get his party on.

The eight-term senator has big plans to ring in his 75th birthday over and over and over again during the next week.

Festivities began quietly Thursday night (his real birthday), when the senator was treated to a romantic dinner a deux by his wife, Vicki, at the Inn at Little Washington. Sources say the couple spent the night at the inn before heading back to Washington yesterday.

Next up: A private party tonight. We're told it's a Kennedy tradition to do a costume-themed bash with family and close friends. This year's motif is movie stars.

The senator can take a breather tomorrow and Monday (no events are planned -- that we know of), before gearing up for his next party on Tuesday. Vicki plans to host another fete with her hubby's work colleagues, Washington friends and a members of the media.

But they're not stopping there: The birthday boy is then heading to Boston to witness the aircraft carrier USS JFK's last port call. Kennedy and his niece Caroline plan to receive the ship and host a celebration.

Things will finally wrap up next Saturday with a birthday blowout for colleagues and friends at the Kennedy Library in Boston.

Noted . . . · The latest on Britney: The pop star is "a sick little girl," her father, Jamie Spears, told Fox News Thursday. "We're just trying to take care of her." He said his daughter's problems{vbar} are "not about what other people think" and that he and Spears's mom are "concerned about our daughter." Spears's estranged husband, Kevin Federline, visited the singer at Promises rehabilitation center in Malibu yesterday, where she is receiving treatment.

· Former Britney Spears "manny" Perry Taylorhas turned up on the red carpet again. The U.S. Naval Academy grad was last spotted{vbar} with Jude Lawin December, but we're told he's currently doing security for Tyra Banks. Taylor was spotted trailing the model-turned-talk show host at events in late January and again earlier this month. Banks's publicist had no comment.

-- Korin Miller