I just remember i did this as a joke, but it's already useful when i'm playing with the notebook while watching TV without my wife telling me that i'm playing the whole day. I took an excel file screenshoot and used it as game background.
Does it look like a game?
The game background is the resource 328 in reshacker, you can use this as the excel background:
http://www.prodeportes.com/fof2k7/bi.../1033excel.bmp
If instead, you want a full black background, use this:
http://www.prodeportes.com/fof2k7/bi.../1033black.bmp
The black one is what i use as the default office one distracts me fom the game, i prefer all black background.