Tim,
I had similar problems about 4 yrs ago, when I built a new ATX system with an AMD CPU (the system I am still using).
It turned out to be a combination of a poorly performing power supply and a faulty CPU.
I sorted the power supply quite quickly but the faulty CPU nearly drove me mad and cost a lot of money as I had replaced nearly everything else until I found it. I finally exchanged it for a new Pentium and the problem was solved immediately.
I suggest you clock down your CPU using the BIOS or board jumpers to see if it reduces the number of crashes and freezes. If it does, it's a good sign that the CPU is bad.
Good luck - always glad to help an old BFTS and UAS mucker! <img src="wink.gif" border="0">