Since it's a new system, you shouldn't have to worry about driver problems for the chipset/mainboard.
The only problem you may run into is some old programs left over from the Win98 days. We have ONE Geneology program that doesn't even like XP Pro, so the so the wife runs that on an old lappy with ME on it.
Mostly, if you are just a home user, and do run ito an application that doesn't like x64, there are generally other apps newer apps that can replace them.
I started using XP x64 in it's beta days, and I've been quite happy with it. I use HyperOS, for running multiple OSs, and started with one install of x64 just to see what it was like. Since then, I've gradually switched all my OSs but one to x64. Now I'm the opposite of where I started. One Xp Pro for the wife, and 5 x64's for me.
Put x64 on your new compy, and add another couple of gigs of RAM while you are at it. I'm running 2 gigs right now, but when the tax return gets back...it's gonna be 8 gigs for me since it's so cheap right now
I thought I'd never need more than 2 gigs, but I installed Fakefactory's Cinematic MOD for HL2 and it needs at least three, and would probably use more if it could get it. I think that's the first time I've seen my system really NEED the pagefile.