Is it just NWN? NWN utilizes an old OpenGL shader that the 400 and 500 series nvidia card hardware no longer supports. Without it, anything that utilizes transparency (cloaks, robes, bows, list goes on) in NWN will annihilate your framerate. The last few nvidia driver releases add this support via software so it isn't a problem anymore, but if you have the old drivers, you still have the old problem.