Just found this via Jeff Sandquist’s blog. You will need the .net2.0 framework for it to work. It checks Flickr for photos with the tag(s) you supply and then uses it as your background. You can set it to change whenever you want.
Very Cool!
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Mark's Musings 
Hello Mark,
the site for this changer is down. do you have the installer that you’d be willing to share. Thanks in advance!