Were to start skinning your UI?
 

I've wanted to skin my UI with something cool, but haven't been able to find anything to my taste (Mainly a cool troll skin) so I was thinking I could just do it myself. But honestly I have no idea how to even start on this. Basicly I just need someone to point my in the right directon (Namley were the UI graphics are located so I can start editing em :P)

Cheers in advanced.