Well, if you have NWN, toy with the tooleset a little.
I think they've done a really great way of managing areas/npcs/scripts/etc.
Basically all npcs have a set of scripts assigned to different events. For instance, if you want to talk to them, script1 will be called. When you attack them, script2 will be called and when you poke them with a stick, script3 will be called. Of course, you can easily change those scripts and assign new ones (as well as define your own triggers).
At the same time, all actions are manage through and action-queue. Quite logical, once an NPC finishes an action, he starts the other and so on. Of course, scripts can assign actions (so for the "onAttack" trigger, you would give the NPC a script that assigns a "attack player" command to him).

This sounds like a really good and flexible system to me :P