I'm familiar with Memtest86, I'll run it tonight while I'm asleep.
Windows XP Professional Service Pack 3 (build 2600)
2.60 gigahertz AMD Athlon 64 X2 Dual Core
Board: Gigabyte . M61P-S3
AV =Nod32
Firewall=Online Armor
4 GB Patriot RAM( two 2 gig sticks with heat spreaders on them.)
Hauppauge WinTV HVR-1600 NTSC/ATSC/QAM Combo
As far as software goes, I notice this has happened when I'm watching a video with PowerDVD.Sometimes I'll pause the video and look something up online and the machine freezes up, but that might be coincidence.
I also watch a lot of baseball using WinTV with PowerDVD paused.
I'm not running any CPU intensive programs.