I'm configuring my new PC as we speak
...
Didn't want to go with Vista yet because I want to play around with vista in a virtual machine or dual boot first + not all my hardware has Vista drivers yet. But I installed 64bit Windows XP which is the same deal when it comes down to your question...
Finding 64bit XP drivers for all the hardware wasn't a problem, only the 64bit drivers for my TV card were a bit hidden on the site.
For over 4GB you really need 64bit, 32bit just doesn't support it. But you can run 64bit with 2GB or less too like in my case. 32bit applications are able to run on a 64bit OS, but there are some problems with a few programs... haven't run into problems myself, but i just only finished doing Windows Update and installing drivers.
/ 
