[Captain Kwok]

The motherboard (asus p4s8x) has good performance and is generally a quality board. Outside of these error, I have no qualms about it.

I think the problem is referred to as a soft or transient error with the RAM - which means my RAM isn't physically bad, but problems with the system timing etc. can cause random errors. Since the bad memory addresses are different with each test, I think this might be a probable cause. However, until I get home later I can't fiddle with the speeds. I've also found some info that identifies a timing issue with the board and the auto setting - so hopefully I can make some progress here.