I'm assuming you mean to turn off the names over the heads of players/npc's. I'm afk at the moment, but I know under options (alt+o for me) there is a setting that specifically deals with player labels/targeting, and I think it was under the user interface category. There are options to change it so names always display, display on target only, etc. I suspect npc's have similar options. I can look it up later this afternoon if no one has responded by then, but I'd recommend playing around with it a little bit to find a setting that works for your situation. For BG's I like bold labels for encounters and large target rings, whereas if you are planning on taking screenshots something more muted may be better.
