Right click desktop -> Personalize -> Desktop Background -> Choose Browse and select the folder with your images -> Now check/uncheck the images you want to use then decide how you would like the images to change and whether to shuffle the order of the slideshow, then save changes and enjoy.
i do not have windows 7 i googled this taken from ehow.com
hope it helps

Dont worry about it Namechange its all good i may be wrong not totally sure since i dont have Win 7
This post was edited by MrNasty on Jun 21 2011 06:31pm