Weird problem any hints/help???

Greetings!
I'm having a heck of a time getting a system I built to work correctly.
I have an AMD 900MhZ Athlon Tbird and an EPOX EP-8KTA2L motherboard--running WIN98SE. I have swapped out memory, drives, cases, etc, etc and still I have the same problem. When the system is under a low load, everything is fine, but as soon as I go to install software or engage in some CPU intensive task, the whole system locks up. I have swapped hardware (drives, memory, cases, cards, etc), ungraded BIOS, new drivers, OS installs, clean drive installs, etc and always the same.

I replaced the MB 2 times, so I doubt if it is that. I disbled the internal and external cache on the CPU and *still* the system hangs.

One thing I am not too sure about is writing to the disk. COuld it be related to something like that? Evidence would be that using Eudora will freeze the system 99% of the time and there are *always* table of contents errors or things like that. True, they could be from the previous time it crashed, but...

Any constrcutive thoughts would be appreciated.

Thansk!