Justin Timberlake sings "The Social Network": "The script was its own song, really."

If he hadn't been selling millions of records when Napster came along, Justin Timberlake thinks he might have been one of its users. Napster was a web service allowing music fans to rip and exchange their own recordings without observing the niceties of royalties and copyrights, and it inspired a celebrated court battle with users charged as thieves and pirates.

"When Napster hit the scene, I was 19 or 20," he told me. "I had mixed feelings about it because I was the same age as all of those college kids that ended up playing the role of defendants in court. Had I not been in the music industry, I probably would have used it. At the same time, I was watching friends in the industry who were songwriters and were forced take up new jobs. All they do is write songs. They don't have endorsement deals or sold-out shows. They were getting a small piece of the collective pie."

There is an irony, then, to be found in Timberlake playing the role of Sean Parker, the mercurial founder of Napster, in David Fincher's "The Social Network," one of this year's Academy Award front-runners. The movie is based on the story of Mark Zuckerberg, who launched Facebook as a Harvard undergraduate and soon saw it become a phenomenon. The real Parker had a similar experience with Napster, and materialized in Zuckerberg's life as a Svengali of the fast lane.

"The Social Network" is on all the lists of Oscar contenders, and Timberlake is often mentioned as a best supporting actor candidate. Justin Timberlake? The perennial Trending Topic on Twitter? Yes, and why not? In one of the best films of the year, he provides a crucial performance, and he does it with confidence, bravado and heedless energy. It's acting. It is also perhaps like nothing many Timberlake watchers expected, but there you have it: Many performers have talents we never see, because they stay within the parameters of their early fame.

For Timberlake, fame was not launched at the Actor's Studio or at Julliard, but on "Star Search," when he was 11. That led to stardom of sorts on the Mickey Mouse Club, and then big time when he became the lead singer of 'N Sync. Then he went solo and started winning Grammys and going platinum, and -- well, nothing at that point could have predicted his casting as Sean Parker in "The Social Network."

Parker is a difficult role. Mark Zuckerberg is played by Jesse Eisenberg as a super-intelligent geek who likes to bash people in conversation. Parker sees him and raises him. This requires an actor with a lot of confidence and agility. Eisenberg, at 27, is very experienced. Timberlake, at 29, is new to the front ranks of feature films, with all due respect to "The Love Guru" and "Black Snake Moan." Yet he embodies the Parker role and sells it persuasively. His Parker is a devious manipulator with a private agenda and an instinct for personal openings. He's a spellbinder. The choice of Timberlake is not only good casting by David Fincher and his casting director, Laray Mayfield, but good casting out of left field.

The Zuckerberg-Parker exchanges are often in a rapid-fire tempo that evokes screwball comedies. I asked if that took a lot of rehearsal.

"Our rehearsal process was, in fact, all talking," he said. "We never once got up from the table. We would go through the scene, just reading it. Then David Fincher, [writer] Aaron Sorkin and the actors who were in the scene would just sit and talk about what our characters were looking to accomplish in each moment.

"For a character like Sean, who was so brilliantly constructed by Aaron, the overall goal was intact. His most convincing trait, as a value for me (and not without irony), was just how literally convincing he could be to a guy like Mark. And when you have the opportunity to do a large number of takes like David likes to do, the dialogue becomes such a part of you. It makes it easier to rattle off a few pages of poetry. Yes, I just referred to Aaron's dialogue as poetry."

I have an additional theory. Later in our e-mail exchange, Timberlake mentioned: "I come from a family of people that think that they are really funny. If it was up to my family, I would be doing comedies forever."

To be funny, you have to be smart, think fast, talk fast, and have flawless timing. Those are Sean Parker attributes. Maybe Timberlake began to form them doing standup in the family living room.

Judging by photos of the real Zuckerberg and Parker, Timberlake looks something like each of them. "But I sense the Parker role was closer to your inner rhythms," I said. "Wrong?"

"The script was its own song, really," he said. "The rhythm of this film was so established by Sorkin. He laid the foundation of this world of hyper-smart college kids. I can't think of a writer working today that could have done a more masterful job. If you're asking about which role I would have preferred? Parker. Hands down. The way that character was written was just too much fun.

"But I felt like these two characters probably suffered from the same fears and insecurities. They both invented something to connect with the world comfortably, too. Mark invented Facebook. Sean invented Sean Parker."

I gather no one on the movie met Zuckerberg. Did you meet, or did you already know, Parker?

"I met him briefly in New York. At the time, I hadn't been cast in the film but it was speculated that I might be playing the role. We spoke for a second and he seemed like a really nice guy."

I observed that Parker has dialog where he brags that he brought the music industry to its knees, and put record stores out of business. There's some irony in a multi-million album seller like Timberland saying this dialog, yes?