I am sorry to say this is currently a major problems for may NWN players out there, myself included. To cut a long story short, Nvidia made a change in their drivers which "broke" the opening menus.
You can find the full details on Boiware's forums here
Neverwinter Nights: Black Screen when launching Neverwinter Nights (Forceware Driver Issue)To summarise, the solution depends on your model of graphics card,
"The current solution for Windows XP users (Using a GeForce 8000 series card) is to roll back to Forceware version 97.94 .
Windows XP users (not using am 8000 series card) can solve the issue by rolling back to 97.27
Windows Vista users (6000, 7000 and 8000 series cards) can resolve this issue by installing the ForceWare 163.11 (Beta Drivers) which support the 6000, 7000 and 8000 series cards. A Windows XP version of these drivers is forthcoming."
Of course, rolling back your drivers that far will have an effect on other games you may wish to play (bye bye Bioshock, for example!). Workarounds suggested include changing your game resolution to match your desktop resolution, minimising and restoring the game at the menu screen or, (as some have suggested) clicking around hopefully!
Of course, we could all just install Linux instead?
Oh and yes, it does cause major problems for the DM client......