Photoshop Elements is absolutely perfect for doing skins and stuff. It doesn't have all the fancy gadgets and bells and whistles that CS4 Extended has, but you would never use any of those for car skinning anyway. You'd be able to follow all the RSP tutorials to the letter with Elements.
In a way, as a starter package, it's better, because there's less confusing stuff to get bogged down with. It's still an EXTREMELY powerful tool too.
