Also here is a pic of Vader helmetless in his chamber, note the tube in front of his face as described in the ESB novel, he breathes thru this when his helmet is off, and possibly even eats. This tube can be seen leaving his mouth fleetingly (it's pretty quick when you watch the scene) when Admiral Piett comes in on him, and the helmet is re-lowered on his head. Nothing needs done about this but since I just saw this pic, this goes with what we were talking about earlier in the thread.

EDIT

Sorry, here is the pic http://img12.imageshack.us/img12/6717/vaderhead.jpg