Lanparty UT nf3 250gb - 1 gig RAM problems

I have legal copies of HL2 and Sid Meier's Pirates that fail to install on my computer. It gives a window's installer error, claiming some .cab or .pak is corrupt or something. It's rarely the same one each try. Naturally I've checked the discs on other machines and they worked fine. So I swapped my dvd-rom, uninstalled sp2, and checked for various BIOS/drivers updates. Replacing the drive didn't solve anything. Hmmm.

Eventually I was able to confirm that if I remove one dimm from my 1 gig pair, the discs install fine. So I swapped a completely different pair of 512 dimms and got the same error. According to my trials and permutations, my computer is only able to install the games with 1 stick of 512mb of RAM. And that's where I have become confused...

Any suggestions? Thanks in advance!

Athlon64 3200
Lanparty UT nf3 250gb (default RAM/CPU settings, no OC)
2x512 VS512MB400 Corsair
ATI 9800 Pro

Thats the weirdest thing i've ever heard (well not really, but it's weird). Would you happen to be using slot 3 when using your 1gb set?

edit : welcome to the forums!

I've used both dimms 1+2 and 1+3. And yes, I agree that it's weird. I'm tempted to go buy a 1 gig dimm just to see how weird this problem might be.