I would start with  ultimate guitar tabs and go to the lessons section and read read read and study study study.
this one is free...

also http://www.youtube.com/watch?v=LmcjAGJOPR0

be sure and watch all of this cause he really gets some very cool strumming stuff going on.
there is tons of this type of stuff up there from hard to easy. this one is kind of hard. but there is a bunch of them that you can get info from just watching.