Problem with video related system lockup II
Also Thinkpads with the ATI 9600 video chip used in T42 and T42p can cause lock-ups.
This happens after about two years of use.
According to http://www.technotaste.com/blog/thinkpad-t42-ati-radeon-9600-driver-and-the-blue-screen-of-death-bsod/ this problem is thermal and is caused by the GPU coming off the MB.
Solution: replace motherboard. Or, remove the keyboard to provide extra cooling :)