Rotate Wallpaper Automatically

[Ollie Killingback]

I've got a number of great pics on my Ubuntu 9.10 laptop.  Is it
possible (well, I'm sure it is, the real question is "how is it")
possible to cycle through the set so I get a new one every time I
reboot?  The ones I like best have all been added to the set of
backgrounds under System|Preferences|Appearance so I guess I need a
script to change which one is selected...  I'd appreciate any help.

Ollie