Acting in commercials since age 4 has given Josh Flitter, 12, a kind of Zen perspective: ''When I didn't get a part, I'd go, 'I didn't get that because something even better's going to happen.''' Sure enough, his 2003 pilot, My Life With Men, wasn't picked up by ABC, but then he landed 2005's The Greatest Game Ever Played. Jay Leno saw it, loved Flitter's know-it-all character, and invited him on The Tonight Show which led to the New Jersey native's next role: ''[Nancy Drew producer Jerry Weintraub] saw me and said, 'I need that kid.' Originally, the part was this gawky teen. Jerry said, 'If you do this part, I'll rewrite the role,''' recalls Flitter, who's also in July 3's License to Wed. ''I gotta thank Jay Leno for having me on!''