As far as I know, for the 2000-2002 Accents, there were two keys. Each key would open the doors, start the car, and open the trunk. There was also a key less OPTION which would unlock and lock the doors and pop the trunk...
Long story short, you should only need one key for this car.
Now is the key you have the original Hyundai key?
Maybe someone broke into the trunk and they replaced the lock cylinder?
Sorry to bump an old thread, but just wanted to update this for people in the future: the key used for the ignition did open the trunk, it just seemed the mechanism hadn't been used in quite some time so it took a little coaxing.