If I forget to remove my wireless mouse transmitter from its USB port, my screensaver doesn't ever come on. This is a Microsoft wireless mouse.
I just started using a wireless mouse with this system. I've confirmed that with the wireless mouse removed, the screensaver does kick in.
Screensaver works fine when using the mouse with Vista laptop.
Also, can you burn images into LCD screen by leaving the same image up too long, or was that just a problem with CRTs?
EDIT: Just did a search an found a description of problem and workaround at Microsoft's support site:
http://support.microsoft.com/kb/913405Installed and tested; problem solved.