I have the problems where occasionally the system will just up and reboot. Ususally when in a 3D application/game (even winblows pinball) or sometime just whenever.

I don't think it's a hw problem as it never happened in Win98 or while I was briefly testing WinMe.

Brief synopsys of system:
Athlon 500
256 MB RAM
300W pwr supply
128 PCI Sound Blaster
MSI 6167 Motherboard
56K 3Com sw modem (eww)
32 MB TNT2 card
3Com 3c905 nic