Well, normally I'd say its your RAM, overheating or your power supply. As you've swapped your power supply, and seem to have ruled out overheating, have you tried the likes of Memtest here for your RAM?
http://www.memtest86.com/
I think it's unlikely to be your HD; if it was, it would probably tell you rather visibly because a Maxtor 80GB drive will most likely be self-reporting. Not to mention that unless you use different partitions I wouldn't expect it to be selective in the applications it fails on. You could try a surface scan disk just to make sure, but that'll take a long time.
If you have a large bandwidth connection the Ultimate Boot CD has a ton of startup utils to test for every conceivable problem. (just google for it)
Edit:
As a slight aside, decent power supplies (which I presume yours is at 600W) offer a certain amount of surge protection internally. Providing it's not a crappy cheap unbranded one, it's very unlikely that a power surge damaged your hard drive cables, especially if the surge wasn't large enough to blow the fuse...
[ 11-23-2004, 10:17 PM: Message edited by: shamrock_uk ]