[{OF}Barney_B]

You know, your problem has sounded so familiar to me and I couldn't exactly remember why so I went to your "It's done sorta" thread and saw that you got the Corsair 2 GB pack. If it's the same part number that I got (TWINX2048-3200C2) then maybe I can give you another option if the ones you are pursuing at the moment don't pay off.
I recently upgraded my system which included the above mentioned memory upgrade and my system immediately started doing stupid stuff like locking up, rebooting for no reason and causing video errors. I was thinking "Crap!!, I just got all these cool parts and one of them is stinko". I slowly but surely ruled out each part until I was left with the memory (I paid serious (for me anyway) cash for this super duper ram) so I went to Corsair's fixit forum and found some ideas and tried them. The one that worked for me was manually setting the values in the bios. Once I did that my problems stopped and I've been happy ever since. Can't say this is what's up with your system but...here's the values I used:

SDRAM CAS Latency: 2.0T
SDRAM RAS to CAS Delay (tRCD): 3T
SDRAM Row Precharge (tRP): 3T
SDRAM Active to Precharge Delay (tRAS): 6T

Maybe this will help you, maybe not. Either way, I just upped my post count!

Really though, Good Luck. I know how frustrating this crap can be.

PS Read the lines in your bios carefully to make sure the lines are the same. The lines in my bios were not presented in the order shown above. Word to the wise.