Undercover Brother

Having fought the Japanese with Nicolas Cage in Windtalkers, Mark Ruffalo has traded army green for NYPD blue. ''I've been hanging with homicide detectives,'' beams Ruffalo, who's researching his role as a cop in the Meg Ryan thriller In the Cut. ''A detective's going to let me sit in the car while he's doing drug deals. They're not supposed to let people go in as deep as I'm being able to, so I'm doing this on the sly.'' The actor, who dons a bulletproof vest on ride-alongs, says his handlers don't even know about his undercover work (uh, until now). Ruffalo's growing a beard as a disguise, though he's not too worried about blowing his cover. ''These guys on the street probably haven't seen You Can Count On Me.''