So you want a skin with areas that are simply put, transparent? Well, this is a highly tricky task. The file you need is called region.txt and the way to do it is a lot like playing connect-the-dots.
Region.txt provides a set of names such as Normal, W ...
//////////
|------------------|
|** S T E E L E D**|
|------------------|
//////////
1.Contains skinz for :-
a.Mainmenu
b.Equalizer
c.Playlist
d.Mini Browser
e.Winamp AVS (Advanced Vis Studio)
f.Cursors
2 ...