The specs for NWN don't say anything about it not being able to run on a 466 MHz machine...but it does say it requires some video RAM and at least a 3rd generation 3dfx card. The meat of the game ain't gonna be in the graphics, it'll be in the game. And besides, with NWN's designer toolset, you'll be able to make BG III yourself!
check out the NWN website at:
Neverwinter Nights
Mourn Yauntyyr
(Who will be giddy as a little schoolgirl when NWN finally comes out)