Thanks for your reply. Yes, XP SP3. Yes, it is overclocked but it passes a long prime95 test. I checked ram with Memtest 86+ overnight immediately after I built the box but not since overclocking. However, the memory is running at the stock frequency.
This is an HTPC box and the crash happened while watching ESPN3. I am using the onboard video with a passively cooled stock heatsink on a Foxconn 740G based board. Could this be the problem? IGP overheating? However, after the crash I restarted and have been watching ESPN3 without more problems for a considerably longer time than when the crash occurred.