Look no further!
To change the skin is quite easy actually, it's a straight forward process.
First up you'll need to find a steam skin you want to use!
This is a great thread with a collection of skins:
http://forums.steampowered.com/forums/showthread.php?t=1161035
Download the one you want and extract the content with your favorite extraction program (I use 7Zip)
You should now have a folder with the name of the skin, drag that folder here:
%steaminstallation% /skins
It should now look something like this:
(I have 3 skins in the folder)
You are now pretty much done!
All you have to do now, is start up steam
Click the upper left button called "Steam" then "Settings"
Go to the "Interface" tab
Under "Select Skin", select the skin you just installed.
Now restart steam and the skin should now be in use!
