Upgrading to Windows 8 was probably the best thing I've done for my NWN installation. The game is running quite nicely and I don't need to use any of those silly compatibility modes like I did with Vista and Win 7.
My system specs are nothing special - maybe that's the key to success (at least in my case)...
Win 8 Pro 64-bit
Intel Core i3 550 CPU @ 3.20 GHz
6.00 GB RAM
nVidia GeForce GT-240 (w/ 1.00 GB VRAM)
Anyone else care to weigh in?