There is one more thing to look into that I have heard is an issue on other games, but didn't know whether it hit NWN. My understanding of the details is rough, so what follows may be off a bit...
Windows tries to lock folders in the \\Program Files (x86)\\ path after installation so that installed software can't install other software there. In theory, this helps protect from viruses. Newer programs instead keep any new files or changed files needed for program customization in the \\Users\\
username\\AppData\\ path or \\ProgramData\\ path.
Apparently, to accommodate older software that likes to make changes to its install folders after installation, Windows can employ "virtualization" put the files in a parallel path inside one of the paths I mentioned and try to reroute calls to those files to the new paths. It usually includes a way for the users to get to such files by putting a "Compatibility files" button in the original folder. Unfortunately, the system doesn't always work in that the software doesn't always see the files in the virtualized folders.
Like I said, I am not sure if this is what you are encountering, but I know people playing other older games have run into issues with it and the symptoms are similar. I think the easy way to check is to open the folder where the files are supposed to be and see if the folder has a "Compatibility files" button. If it does, it could be that the files aren't really where Windows led you to believe they were.
See
http://support.micro...kb/927387/en-us for a little more on virtualization and some problems people have with it. One workaround might be to run the game as adminstrator. I do that anyway so that I can can around the annoying UAC warning everytime I try to start up. You may also want to check that you have the correct ownership and access permissions for the game folders.