The game often will crash to desktop during the splash/ company logo phase of starting it. I will normally need to restart it 3-4 times before it gets to the menu and is fine after that.

If the intro movies/developer screens are your problem, you can disable them in your nwn.ini file under [Display Options] by setting Disable Intro Movies=1.

And I'm guessing you already done/tried all of this also:
http://www.gog.com/en/forum/neverwinter_nights_diamond/game_will_not_run/post27

Old sound drivers can often be a problem too which no one has mentioned yet. Especially if you have a realtek card/onboard sound.

Good Luck :)