Wandigo is a free multi-monitor wallpaper tool for Windows. With Wandigo, you can set a separate wallpaper for each monitor easily.
Add folders and images for a monitor;
Manage each monitor separately;
Resizing options for wallpaper images;
Set background color;
Shuffle the images or set in order.
Wandigo is intended for users with a multi-monitor setup. However you may want to use it for its slideshow feature on Windows XP even if you have a single monitor.