Mobo or Memory problem?

Hey guys I joined this forum hoping someone can help me out. I built a new computer for my wife a few months ago and it randomly blue screens. It didn't become such a big problem to me til I started using the computer more often. I have recorded 5 different reason for the BSODs so far. They are: PFN List Corrupt, IRQL Not Less Or Equal, Memory Management, Cache Management, and the one I got today was System Services Exception. I read around on other forums and found that its most likely a mobo, memory, or HD problem. Well I'm using two 1 gig sticks of ram and I did vista's memory diagnostics test on each stick by itself in each ram slot and came up with nothing and I also downloaded Everest and checked the SMART senors to see if it might be the HD and nothing stood out of the normal there. I'm at a complete loss of what to do now. I'm suspecting it might be the mobo, but I want to keep the computer cheap and not buy a replacement I don't need. Please let me know what you guys think. Here are my system specs.

AMD X2 4000+
ASUS M2A-VM 690G mobo
CORSAIR XMS2 2GB (2 x 1GB) DDR2 800 (PC2 6400) Model TWIN2X2048-6400C4
Western Digital Caviar SE WD1600AAJS 160GB 7200 RPM SATA 3.0Gb/s HD
Nvidia 8600GTS
Thermaltake TR2 W0070RU 430W Power Supply
Vista 64 bit home premium

Thanks in advance.

I already did that and both sticks came up fine no matter what slot I put them in. I tested them together and individually.

It could be ram or PSU, but since you failed to list your PSU, who knows.