For Mark Wahlberg, his Oscar-nominated role in "The Departed" doesn't seem much of stretch. In it he plays a Boston cop, and, really, all he probably had to do was remember the gentlemen who arrested him in his days as a juvenile delinquent in Dorchester. But he gave the movie a lot of its authentic sting. And authenticity, of course, is what can break Wahlberg and, as of recently, make him. From his days as rapper Marky Mark to his stretch as a Calvin Klein underwear model, through all his cinematic misses and hits, it's taken Walberg time to figure out who he was and how best to make it work onscreen.