script to change background in X windows?

[David Piniella <dpiniell@newssun.med.miami.edu>]

I'd like to have a script/program that changes the background between a 
set of images (jpgs, pngs, etc) at either a set interval or login. Is 
there anything like this already? I did a quick google, but found 
nothing. I'm sure I could bash a script out to do this, but would rather 
not if there is already something like this. Any pointers would be 
appreciated,

thanks,

--
David Piniella
University of Miami