Wallpap1

Kelly Software - Wallpap1 - a great freeware wallpaper change program!:

"This program sits in your system tray area and allows you to choose a directory of images you want to use as wallpapers, and Wallpap1 will automatically update your wallpaper using the images in the directory you specify and at the cycle/interval you specify. It supports GIF, JPG, and BMP. You can also set it to minimize/start on start-up, stretch/tile/etc, and rotate them randomly."