Is this a first install on this pc? Was it already installed, working fine before and stopped? If so, did you do any recent changes to your pc?
Have you tried setting your game to video compatibility mode? It will downgrade trying to view .dds textures down to .tga textures which are easier for the card to translate.
If it is already in compatibility mode, you may need .tga textures for the custom content included in the CEP and Ravenloft haks. That will be more difficult to address.
Something else to try is increasing the cache for your game (not just video cache.)
You can up the amount by changing the nwnplayer.ini setting under [Game Options] and adding "Max Memory Usage=64" (the game's default is 16MB, so you could set it to 32MB, or a usable max of 64.)
You should do this change anyway if you have the spare memory to run it, since it will improve your game experience.