Photoshop CS is the best, and also the most current version I believe. Id agree with DLing the 30 day trial before you go spending any money. A lot of people get intimidated by photoshop and give up so a trial is a good idea
i'll be honest, i'm still trying to figure it out, and it's pretty confusing for someone who's never used it before. there's just so many neat little features to choose from...good thing i am doing the free trial right now
Im tellin you the way to go is to do a few basic tutorials. I did like 10 of em and it gave me a good headstart. From there you just have to play with it a lot.