This is pretty much self-explanatory. I want a setup where every, say, fifth time I boot into my Windows install or my Linux install (same computer), my wallpaper changes to the next image in a particular folder on my hard disk. I want it to fill the screen in stretch mode. I run Windows XP Pro and Debian etch with Enlightenment 0.16.7.2-5 and X.org 7.1.0-19. Just a single monitor this time.