the biggest problem is not 32/64 bits version, it's directx capabilities
good old Winxp is directx 9 only, the game is made for directx10, your video card can handle it too
also you may have 4gig install but winxp will only manage 3

Thank you for you comments
Your saying 32 bit will look just as good as 64 bit? as 16 bit will look as good as 32 bit? with this sim being 64 bit and I only have 32 it should take less ram to run and it will not unless on low settings and that looks bad.
I as so have dx10 on this pc.