Visually and performance wise the difference is nil.
Betwen 64-bit and 32-bit the only difference is that:
1. No 32-bit firewalls work with 64-bit.
2. No 32-bit virus protection works with 64-bit.
3. Most 32-bit drivers do not work with 64-bit.
But if you are willing to use say, Grisoft's AVG w/firewall (64-bit compatible) or Nod32 for virus protection, you will be fine.
As for drivers, you can find many 64-bit drivers on PlanetAMD64. I am using a beta HP driver set for my printer. An Atheros driver for my D-link wireless card.
It can be done, and personally I think the benefits are worth it.
I have only had to reinstall XP64 once in just over a year. I have had 2 maybe 3 BSOD. in that same amount of time More often it is a hard crash
from hardware failure than OS failure. A;so most (not all) spyware does not work on XP64, but most spyware removers work on XP64.Also bundle it with firefox and AVG, and you would be pretty must immune to most baddies.
IMHO XP64 is that last OS I will need until Vista has gone through rigorous Post-Beta testing, which should be sometime around 2009.