Do you mean the elven rangers patrolling around the talking tree?
If you cast Poison Cloud near (but not directly on) a friendly NPC, you can do damage without them turning hostile and counterattacking, and without loosing any reputation. Most (maybe all) essential characters are protected from being killed, but you may want to avoid attacking named NPCs, just in case.
Level 5 of Know Creature will give you the resistances of an opponent, but as a warrior I never bothered with it. Mages may need to be selective with attacks, but steel works on anything. <img src="/ubbthreads/images/graemlins/biggrin.gif" alt="" />
