As a follow-up - I ran several tests on my entire laptop. They didn't report any errors. (I was relieved about that, but still frustrated why I couldn't work for more than 3-4 hours without having to reboot due to video errors).

I disabled fastwrite, which still didn't help.

I found an article on MSDN about conflicts between the ATI driver and XP (prior to SP2). So I unintalled the ATI driver and went with a generic monitor at 1024x768. That was Monday. Haven't had an error since.

Thanks,
Kevin