4GB Problem on Windows XP SP2

Okay yesterday i just bought an additional (2 x 1GB) of ram on ebay.DDR2 6400 OCZ @ 800 mhz.when i added them on with the other 2 gb(2x 1G) i had on(all ram are the same) i get BSOD randomly also when i went to play games it appeared after a while.i removed the 1 gb stick and the computer works fine.I called ASUS (I have striker extreme) and they told me that its not a mo/bo problem but microsoft’s and told me that there is a patch on microsoft that fixes this.Could someone help me?

Computer info:
Asus striker extreme
BFG 8800 GTX OC2
500 GB SATA2 16 MB
200 GB SATA 8 MB
OCZ PC 6400 SOE 800MHZ
CORE2DUO 2.66 ghz