Starring roles in movies like To Live and Die in L.A. and Manhunter plus an array of TV and theatrical work may have briefly grabbed the attention of some of William Petersen's Chicago-area relatives, but it wasn't until CBS's CSI: Crime Scene Investigation took to the air that the actor's extended family really began to follow his career.

But as Petersen explains, he's been hard-pressed to answer his clan's most frequently asked CSI-related question: "'Are you going to have sex?'" The actor, whose forensics officer Gil Grissom spends more time in the lab than between the sheets on the Golden Globe-nominated drama, told laughing attendees of the Television Critics Association press tour in Pasadena, Calif., "I don't know. He is a nerd. I don't know if nerds have sex or not."

Their lusty activities may remain in question, but Petersen sure enjoys the enlightenment the investigators who serve as advisors to the series are able to provide, particularly when they help him hide his own technical shortcomings. "That's been the most remarkable thing — getting to deal with these real-life CSIs who work on the show with us, getting to deal with their stories and with the kind of knowledge that they have that I never had," he said. "I was terrible at science, terrible at math, all those things, so it's a real opportunity for me to live another life."

One thing Petersen and his show are decidedly not terrible at is drawing an audience. Enough of one, in fact, that beginning Feb. 1, CBS executives are moving it to Thursdays at 9 pm/ET, a post-Survivor slot that pits CSI against NBC powerhouse Will & Grace.

A big part of the network's confidence stems from the surprising number of women tuning in to the often creepy series. Petersen believes he knows why CSI is such a hit with the ladies. Deadpans the actor: "[It's the] really sexy men."