BY GLENN WHIPP >Staff Writer

`The Rocker" has Rainn Wilson (above, right) banging the drum for two very different rock groups. Bounced from an '80s hair-metal band just before it made it big, Wilson's Robert "Fish" Fishman has been nursing a grudge for 20 years. A second chance for immortality arrives when his high-school nephew reluctantly offers him a gig in his emo band, A.D.D.

"Fish is a capable drummer, but his hair-metal excesses kind of get in the way sometimes," Wilson says, adding that the movie's PG-13 brand of sex, drugs and rock 'n' roll is more akin to "Say Anything" than "Superbad."

Wilson ("The Office") did all his own drumming in the movie,` spending an intense few weeks learning the instrument before beginning the film.

"I'm pretty mediocre," Wilson brags. "Most of the lessons were just to get me to embody what a heavy-metal drummer does - filling the stage, connecting with the audience, getting that primal pulse down."

That said, Wilson now understands a little about what makes drummers tick.

"Drummers, I've come to realize, are just big monkeys," Wilson says.

"Big monkeys with sticks in their hands, pounding on things. It definitely takes a certain mentality sitting back in the corner and making loud noises. It's very cathartic."

Wilson made "The Rocker" while on hiatus from Dunder Mifflin. Prior film work included supporting turns in "My Super Ex-Girlfriend" and "Juno." Even if movie stardom isn't in the offing, he got one permanent benefit from "The Rocker" - the kick-ass drum kit he used in the film.

"It's in my garage," Wilson says. "I still bang away on it. So does my 3 1/2-year-old son. You can't believe how much sound it gets. My neighbors can attest to that."

>Glenn Whipp