XP is a 32 bit system I believe. 32 bit systems can only use 3.5 G ramm and 64 bits use upto 5.5(?) - Im not too sure on the numbers but you get the jist.
The XP support IS being implemented and was a goal which the devs are still trying to reach - in fact its one of the delays in the patches we are waiting for! There was no readme in the last patch so I dont know if you should be running the stock 1.5 or the beta patch 1.08.
I know vista stank but serious you need win7 - its 2012.
