Demetri Martin He has the lead role in 'Taking Woodstock,' a big part opposite Brad Pitt and a few minutes left over to tell jokes. Stand-up comedy is the kind of training ground that can propel you skyward (Jim Carrey, Robin Williams) or leave you toiling in nowhere towns (almost every other joke-teller out there). Demetri Martin still does the occasional comedy gig, but the 36-year-old humorist carries much more on his plate these days: In addition to the starring role in Ang Lee's nostalgic drama 'Taking Woodstock' (Aug. 14) and a plum part opposite Pitt in next year's baseball story 'Moneyball,' Martin has a Comedy Central television series -- 'Important Things With Demetri Martin.' Altogether, it's an unexpected outcome for a Yale-educated historian (senior thesis: the role of women in Greek immigrant communities) and law-school dropout ('I wanted to be a lawyer since seventh grade') who not that long ago was best-known for his online 'The Jokes With Guitar' video. Indeed, it was Martin's YouTube appearances that caught the eye of 'Taking Woodstock' producer and screenwriter James Schamus. 'I thought this was the most original, interesting comedy I'd seen in years,' Schamus says. 'And it wasn't mean.' Several months later, when Lee started casting 'Taking Woodstock,' Schamus mentioned Martin, and the director promptly picked him for the lead part as Elliot Tiber (the author of the memoir upon which the film is based): a young man stuck in his parents' run-down motel, which just happens to flank the nation's most important music festival. Martin, who recently moved from Brooklyn to Los Angeles, admits he isn't a trained actor and has much to learn about show business. Comedy, he says, remains his 'first love and primary interest,' but he concedes that steady film and television employment has its benefits. 'It would be nice,' he says, 'to be in one place for a while.' -- John Horn 