Reboot. It’s the first step always.
What program were you running at the time?
It could be an outdated or corrupt driver – It is a good idea to reinstall directx as mentioned earlier.
Try this windows support site: http://support.microsoft.com/default.aspx?scid=http://support.microsoft.com:80/support/kb/articles/q267/8/58.ASP&NoWebContent=1
It’s about “memory could not be read”, I’m not sure that it’ll fit your problem, but it’s worth a shot.
Doncha just love computers?