Well, it's an Athlon 1000, which runs hot. It's also got crappy fans. Finally, it's got a Hitachi Deathstar, which puts out about a million BTU.
I moved one fan to blow directly across the underside of the drive (top side is insulated and stays cooler). I added 2 more fans and swapped the P/S for a slightly better one, then reinstalled the OS and it's all happy. It's been up for about a day. But, I'm leaving the case open for now.
It's a PC Chips M863G v1.5. It had 256M of DDR400 and I had a 128M DDR400 to add to it.
The drive is 7200RPM 80gb.
I can't add USB devices to the boot list, but I can go to a boot menu which will let me choose them.
So, assuming it's all good, this will be the kids' computer.
I called it Mesa Blanca