I'm at work, so only one or two quick remarks here: the head is one actor (not including eyes, gums/teeth and tongue) and will stay that way. Making face morphs would be a pain if the face consisted of multiple actors. There are upper and lower jaw actors as well which contain only the respective gum and teeth geometries. Since the face is one actor, making just the lower lips follow the movement of the lower jaw is probably impossible with Poser's rigging system, or at least very, very hard and not really worth the effort.

@Laurie: you should take a look at Wings3D. I can simply hide geometry that's in the way and it won't be influenced by whatever I do. That's how I modeled the whole mouth including teeth and gums in one piece. There are various ways to make sure you select exactly the portions you want to hide. it takes a bit of practice to learn how to use Wings, but as far as I am concerned, it's totally worth it.

-- I'm not mad at you, just Westphalian.