Yeah, if you can check from your old computer, there should be a text-file named "nwncdkey" in the game folder.
This is the best, and possibly easiest way to do it. Assuming you still have your old computer, just plug it in, go to c:/neverwinter nights/NWN (that's the default directory it is installed in,) and look for the file called
nwncdkey - it will have a list of keys, 1, 2, and 3, representing Original, SOU, and HOTU, respectively.