XP 64 bit is garbage. Either go XP 32 bit or if you NEED (and you don't unless you are hard set on 4 gig of RAM) 64 bit, go Vista.
For the motherboard, try to go with one of these chipset's:
P35, P965, 680i, 650i.
These are by far your best 4 choices.
Intel just had price cuts so you would be...