Don't know about KOTOR, but you have purchased the right game if you want to play real D&D online, within a game that is, for D&D can be played anywhere, and by many different mediums it may be played, even on forums, pen & paper, or through a chat window / software client..
NWN is without a doubt a great place to learn the core game, because in truth, you will learn a lot from playing NWN about D&D..
Nevertheless, since your on Windows 7, after you install the game, right click on the Diamond Edition icon and select properties, then select the Compatibility Tab, then make sure you run it under XP Service Pack 3, furthermore, you want to disabled visual themes & desktop composition as well, this should help you have a good experience.
Finally, make sure you set the resolution of the game to the exact resolution of your desktop display resolution, therefore if your using 1920 X 1080 @ 60 Hz, your game resolution should be the same as well, and you may have to manually set this when you configure it for the first time, using the configuration button when the game first starts... (Select Manual)
Hope this helps
