Two heads are not always better than one.

Just ask Sam Rockwell. He plays the two-headed President of the Universe, Zaphod Beeblebrox, in The Hitchhiker's Guide To The Galaxy.

"It was really a pain in the ass," he says, about carrying around an extra head. "Really weird."

Hopping up to demonstrate the rigours of balancing a fake head, Rockwell throws his chin out and his head back and pretends to stumble around the room. He says, "We tried to avoid CGI. We tried it two ways, with a prosthetic on my head, and then the second way was me, live. Mostly, I went around and I had to do these movements looking at the ceiling and a lot of time I'd bump into things. Thank God it was minimal," he says, laughing, "because it was hard."

The Hitchhiker's Guide To The Galaxy opens here Friday. About creating his character, Zaphod, Rockwell says he threw in a little Freddie Mercury, some Bill Clinton, a pinch of Vince Vaughn and some Elvis Presley. "There's some George W. Bush in there, too," he says. "That bravado and arrogance. Like, when he says, 'I'm president of the galaxy, babe. I don't have a lot of time for readin'.' "

Rockwell, 36, is the son of actors and has been an actor since he was 10 years old. The cool guy's cool guy, he's had roles in more than 40 movies and is currently part of a Gulf War marine outing called Jarhead for Sam Mendes. Rockwell says he was too old to go to boot camp. Anyway, he's done that.

About acting, he says, "I don't really know how to do anything else. I don't have any skills. This is it. This is all I got and I'm still learning how to do this. You have to have no choice than to be an actor. Otherwise, you're not going to make it -- not in anything that's that competitive."

Pointing out the connections between his films and how one led to another, he mentions Box Of Moonlight and Confessions Of A Dangerous Mind as two that meant big changes in his life and career.

"But you know, little things build up. Those things don't happen out of nowhere -- through Safe Men I got Charlie's Angels. And through Green Mile I got Galaxy Quest, and then George Clooney saw that and so then I did Welcome To Collinwood, which he produced. Things add up and add up."

Indeed they do. George Clooney directed Confessions Of A Dangerous Mind and insisted that Rockwell star in the film even though Johnny Depp was one of several big names interested in the role.

Rockwell has done a lot of indie movies, including Lawn Dogs, Jerry & Tom and Drunks. "But by the time I got Confessions, I'd done a lot of leads in movies nobody saw. Like, movies you've never heard of. Ever heard of Jack And His Friends?" he asks, making his point. "No! There you go!"

He was the lead in his first movie, Clownhouse, says Rockwell, cheerfully describing the movie's ludicrous, escaped inmates-of-mental-institution plot. "And then you go back and start from scratch. I do a lead and then go back to New York and work in a restaurant. I did Teenage Mutant Ninja Turtles and then I'm a busboy, and I get recognized. That's a surreal experience, when you're working in a restaurant and someone recognizes you from a movie."

He had all sorts of jobs between acting gigs. But, says the actor, he got lucky, because he got commercials. "And that's like winning the lottery. You do one Miller beer commercial and you've paid your rent for the summer. Getting those cheques in the mail was like, it was glorious.

"I was delivering burritos for Harry's Burritos on a bicycle. That was my last job-type-job, and I got this beer commercial. And then I did this movie with Ben Affleck called Glory Daze. And there have been ebbs and flows, but I've pretty much worked steadily ever since."