If you want to steal stuff without getting the NPG's pissed at you, carry around a chest in your inventory. When you see something you want from a cabinet or chest or something, and the NPG is in the room, open the cabinet or chest, then open the chest in your inventory and move the goods from the open cabinet/chest into the open chest in your inventory. The NPG still thinks the goods are where they're supposed to be and are none the wiser. When you are in some place where you can't be observed, move the chest with the stolen goods in it from your inventory to the ground, open the chest and click on the stolen goods to move them into your inventory - Voila!
<img src="/ubbthreads/images/graemlins/freak.gif" alt="" />