Nah, it is not memory related.  As I mentioned, it has occurred over the span
of many years on numerous computers and builds. Single core, HT single core,
Dual Core, Quad Core, etc.  I don't know what diagnostics you would suggest,
but these computers have all been throughly tested using Prime, Orthos,
Memtest,OCCT or whatever else the flavor of the day for stability testing has
been.  Since the only commonality among these computers is XP, I am quite
certain the problem lies elsewhere.  The memory diagnostics are a good
suggestion for someone who has not ruled this out. 

I'll give 3.33 another whirl, but I don't think it will help.