Quite fittingly, a bittersweet Beatles tribute pervaded last night's Hollywood premiere of "I Am Sam," the tale of a mentally challenged man Sam (Sean Penn) who has to fight for the custody of his young daughter (Dakota Fanning) with the help of a neurotic, self-absorbed lawyer (Michelle Pfeiffer).

Because Sam is a huge Beatles fan (he even names his daughter Lucy Diamond), the film's score is wall-to-wall Fab Four, with Beatles songs updated by today's top artists such as The Wallflowers, Aimee Mann, Sarah MacLachlan, Rufus Wainwright, Ben Harper, Eddie Vedder, Ben Folks, The Black Crowes, and Nick Cave.

At one point in the film, Pfeiffer's character tells Sam that her favorite Beatle was George Harrison, the quiet one. At the film's after party, producer Ed Zwick ("Once and Again," "Traffic") talked about the touching reference, which drew quiet tears from the packed audience at the Academy of Motion Picture Arts and Sciences.

"That had been in the script for five years, but obviously tonight it took on added resonance," Zwick said, adding, "This is the first film to really use Beatles music appropriately because it was so intrinsic to the story." He's not kidding. Even the film's tag line is "Love is all you need..." a line plucked from a Beatles song.

Zwick, who had broken thumb still in a cast from playing soccer with his 16-year-old son, explained the groundbreaking soundtrack: "When you get Sean Penn in a movie, it becomes easier to attract so many people who want to work with him. He is an old friend of Eddie Vedder, and he called him up and asked him to be part of this. Before we knew it, we had Sarah MacLachlan and The Black Crowes and on and on."

Pfeiffer, looking stunning at the after-party in a black velvet dress and coat from Armani, couldn't decide on her favorite Beatles tune. "I don't think I have a favorite. There are just so many I love. This is the first time I have seen the film with all the covers and they are so wonderful," she said

Her 8 year-old costar Fanning, though, thought of her favorite instantly: "Act Naturally!"

The filmmakers and friends - Ed Herskovitz, Laura Dern, "West Wing"'s Richard Schiff and Dule Hill, Christine Lahti and her husband Tommy Schlamme, Mary Steenburgen and hubbie Ted Danson, and even Benicio Del Toro - mingled at the after-party in the Academy's main lobby until late.