In many ways, Justin Long owes his career to Vince Vaughn. Not only did the actor take Long under his wing while filming Dodgeball, but he cast the 28-year-old in this summer's hit The Break-Up. Now that the Frat Pack pledge is front and center in Accepted (out Aug. 18), who did he emulate? You guessed it. ''I found myself channeling Vince,'' says Long of his motivation for Bartleby, a teen who creates a fake college when all the real ones reject him. ''Vince is a natural leader, and I'm not.'' Perhaps, but Long's got a knack for playing the awkward goofball (see: Galaxy Quest, NBC's Ed), a talent he'll show off in Mike Judge's Idiocracy, out Sept. 1. Despite the budding film career, it's his role as a Mac on those ubiquitous Apple Computer ads that has earned the Connecticut native the most fame. ''If ever I was getting any arrogance about being in movies,'' he laughs, ''I've been swiftly brought down to reality. It may be karma for making fun of the Dell guy.''