Jack Nicholson hasn't been known much for comedy lately, but reports say the actor is currently reading a stack of humorous scripts in search of a likely prospect for the production company he's started. If things had gone according to his original plan, Nicholson's company wouldn't have time to be planning any comedies, but there's been a delay in starting "Napoleon," the drama that was to have been Nicholson's main concern these days. "Napoleon," it seems, has been delayed because it doesn't have a screenplay yet -- director Robert Towne has been hired to script the film, but Towne is tied up on "Mermaid," a comedy produced by Ray Stark and starring Warren Beatty. Until the "Personal Best" director wraps up that project, he won't have time to finish "Napoleon." In the meantime, Nicholson is in Los Angeles poring through comedies -- and, incidentally, developing an interest in rock 'n' roll. Last Friday, he was seen lolling around the backstage trailers during the Who's performance at the Los Angeles Memorial Coliseum. Two days later he showed up at the Rissmiller's club in the San Fernando Valley to watch singer Warren Zevon's Halloween performance.