It's not a matter of it being too old. It's a matter of NWN being extremely shitty for a lot of modern computers. So even if it runs comparable games well, there were a lot of issues with NWN that might make it more of an issue than other games.
NWN2 is the one that manages to bring down even modern computers. The original isn't that bad....
Look at the forum for the game :-p. Pretty decent amount of people with large issues. Granted, some of them have easy enough fixes, but for a guy that can't even figure out his computer specs they may be hard to pull off. NWN2's issues tend to be more game breaking, but there's lot of small issues plauging NWN these days.