Copy this crap to your desktop.ini file inside the folder you want to add teh background to, you have to use the address bar to get to it, it's hidden.
--------------start copying after this line, young padawon---------------
[.ShellClassInfo]
IconFile=put your icon dealie here, look below
IconIndex=0

[{BE098140-A513-11D0-A3A4-00C04FD706EC}]
IconArea_Image=put the path to your image here if it is in this folder or any of it's subfolders go like this:  'gabuin.bmp' or  'subfolder\gabuin.bmp' no 's though. and it doesn't have to be a bmp.