2 Tools that are a MUST are:
NWNMax (THE #1 NWN Editing too)
http://nwmax.dladventures.com/
This has loads of tools too (Tileset tools mainly)
http://velmar.dladventures.com/veltools/
Yeah, I never even played the single player game of NWN at all.
I just like making content..
I started modeling/skinning waaay back when Quake 1 was released, and made GI Joe skins
Like Storm Shadow, and stuff. looked freaking cool.