Okay, in this case i'd probably suggest asking the appropriate *buntu people who are responsible for the graphics system for more assistance here. It is possible that a number of factors could be causing the GPU to hang.

Thanks once again. I've started a thread at www.kubuntuforums.net. I've actually posted there once before and received an excellent and quick reply. I'm reticent to try ubuntuforums.org again, though, as I don't usually get replies there. I guess I could try askubuntu.com too, if I get nothing useful. Cheers.