I've made a python script that changes the background every 60 seconds, you can change that in the script...
Make a directory in your home named back (or change the script) and put your background images in that directory to gether with the background.py..
Install feh (in ubuntu sudo aptitude install feh) and run the script.
I made this for openbox and i know that kde and gnome have this option included. If any problems or questions please post a comment.
P.s. Sorry for my very bad english