I just followed this procedure for 9.04, and it worked for me:
open a terminal and paste the following:
sudo mkdir /usr/share/backgrounds
type in your root password (if asked), then paste in:
sudo apt-get install xscreensaver xscreensaver-data xscreensaver-data-extra xscreensaver-gl xscreensaver-gl-extra
After it finishes installing, navigate to ~/.kde/Autostart/
(using either command line or GUI, whichever you prefer)
create a file called xscreensaver.desktop
paste in the following five lines:
save and exit, and you should be good to go!
hope that helps!