Ok.. We are experiencing hard lockups.
How many sticks of RAM do you have?
Do you have a floppy drive?
I have two sticks of RAM, both are identical 512 MB sticks and they're normally in a dual channel setup. However, I've tried running in non-dual channel, placed in different slots, and individual sticks, but my computer still crashed in all cases. Yes, I have a floppy drive, but I haven't used it it ages.
Funny, I have the same prolem. My desktop froze whenever it felt like. I found out that the problem was my Netgear wireless adapter. Installed the latest drivers and everything else but couldnt resolve the problem. Maybe you could find the thread somewhere here - It's called XP Boot Problem (If I remember clearly.)
You could try some of them steps and maybe you'd have better luck.
Hmm, come to think of it, I am using a wireless network PCI card. At college I have it disabled and plug directly into my router via cat5, but at home I enabled my wireless, and I didn't have this problem until I got home. However, I use a D-Link card.