In music, there are few things more insane than an amateur going and trying to sit down with a real player. But that's just what John Hockenberry did earlier this week, when he went to the house of comedian, author and banjo aficionado Steve Martin. A documentary called "Give Me the Banjo" airs tonight, and is narrated by Martin. But in the comedian's New York City apartment, talking about the banjo — as well as Martin's long career in comedy and interest in music — was augmented by some performance and a lesson or two.