Heya!
I have an AMD64 also and it works great with no conflicts nor problems.
I run it under Win x64 sometimes, usually when I forget to dual boot, and it works just fine on the x64 version of Windows.
As for other games, I've had a mix successes and misses - mostly with the more modern games, Civ 4 nor HL2 ran at first but after a few Windows updates and NVidia updates, they're working right - not to mention that HL2 now has a native 64-bit engine (I think, long time since I haven't played).
If I may, install dual boot on your machine just to be safe when it comes to driver and application selection. 2x 10Gb partitions for Win XP and Win XP x64 and a massive one for the shared files (such as NWN). With the price of today's HDDs, allocating 10Gb to a partition that you don't usually use isn't that big a deal if you're shelling out money for a mid-to-high end x64 system.