What version of Mac OS X is running on your G4/400? I know the screensaver won't change until you stop and restart "bgscreensaver" but did you try running bgscreensaver again to stop it? It's kind of counter-intuitive I know, but you double-click it (or click it in the dock if you put it there) to start it, and again to stop it.
If this doesn't fix it, would you be interested in getting the problem fixed? We could do it via this forum, or email if you prefer. Drop me a note back here if you want to pursue it!
Thanks for the feedback, it's all valuable, and much appreciated!
(Version 1.0)