Well here's the answer to this:
System in both cases was an AMD 3.2+Duron, 1 GB DDR LL ram
With a GeForce FX5900 128 MB card NWN2 ran well with these settings:
800X600, low shadows, medium detail, 0 AA, no reflections, 2 light sources per character. It would run at 1024X768, but it was so slow that it was frustrating to play.
With a GeForce 7600GS 512 MB card, it ran equally as well using these settings:
1280X1024, high shadows, high detail, 2X AA, reflections on, 4 light sources, and a number of other (advanced) settings turned up to "medium".
Overall, it was a HUGE improvement, and the game looks fantastic and runs smoothly. I get the feeling even the Camera works better as it now zooms in and pans out smoothly when I would normally be "outside" of something (like blocked by a wall or something like that). I haven't yet faced a huge battle, but I did take on about a dozen enemies at the same time including about 3 spellcasters, and there was no slow down (except for me pushing the pause button

.
I don't know if a 7600GS is the minimum level of card, but since you can generally find it for under $200, I would say it is well worth the investment.