The 64-bitter would be very very very nice. Price being the only problem, assuming that is a problem.
I'm pretty sure a 3200+ 64 beats the schite out of a 3200+ XP. Good job picking a 939, btw.
EDIT: Sorry, but I'd go for a 6800 (regular) its *about* the same price as a 6600GT (depending on where you shop) but offers much better performance. Looks better on specs, too. hah
I'd upgrade your vid card before your motherboard, unless you planned on going PCI-E on a 939 mobo... I dunno.
You're the guy from that hamburger train, right?