Delixe, I found a post on the NWN boards that may have a couple things to try:
"I just finished setting up a new computer that came with Vista, but I upgraded to Win 7, with NWN. I encountered numerous hassles, basically all the ones mentioned in this thread.
Problem: NWN says you don't have DirectX installed.
Explanation/Fix: Some Windows installations come with DX 10 or 11 preinstalled, but lack the older DX 9 updates that NWN requires to run. Update DX to get the old drivers, you can use this download:
Click Here.
Problem: NWN loader opens, but the the loadscreen never appears when you click 'play'.
Explanation/Fix: Win 7 has new security features. I'd comment on them, but I'm so new to them that I lack the perspective to say anything intelligent. You need to run the program as an administrator. You can actually set it up to run that way every time, by right clicking on it and selecting Properties. I also gave my user 'Full control' under permissions, for all the NWN exes. This stopped issues with the normal play screen not loading, and with F9 testing in the toolset not working. I did the run as administrator and full control permissions on all the nwn exes, and those problems were resolved.
Problem: You have a 7900 series nvidia, the best nvidia card for playing NWN, and the latest nvidia driver setup package (196.21) is telling you it can't find drivers for your card.
Explanation/Fix: I wish I HAD an explanation. As for the fix, using the update drivers option in Device Manager worked. Using only the default, insta-installed drivers that Win 7 forces on you if you don't have drivers intstalled for th card, you get no 3d rendering; the toolset will refuse to open, and I got 0.8 frames per second in a small area with nothing in it in gameplay. With the updated drivers accessed via the DM update option, I got 118 FPS in that same area...acceptable. Hopefully nvidia will straighten this out soon."
Likely most of this doesn't help, but perhaps there's something in there that will get the bloody thing working for you.