The CARD is neither 64 bit nor 32, but I would expect that the drivers should be available in 64 bit, if they aren't already.
http://www.ati.com/support/drivers/winxp/radeon-xp64.html - BETA Catalyst 64bit drivers, and by many accounts, pretty rough in performance - but there should be later releases by the time it matters
The problem you may find is that INTEL CPU/Chipset solutions are looking toward PCI Express instead of AGP - with NO AGP SLOT.
Some other chipset makers may do dual, and it looks like current AMD64 boards are AGP.
The 9600XT will not be any worse in 64 bit (at the moment, it WILL be worse, as the drivers are not up to scratch) - in fact, if they do a good job on the 64 bit drivers (not yet!), it should be better, just so long as you actually have an AGP slot to fit it into!
It's not top of the range - there's the 9800/Pro/XT (it'll probably beat the 9800SE) and the new X800 above it - to be released in (it seems) both PCI Express and AGP, the X800 could be said to be designed for 64 bit - though the AGP versions would run with 32 bit systems.
