You don't need to separate the head and body skin, nor do you need to remap or regroup anything. Just find the templates (they are on the original CD somewhere) or make yourself one with UVMapper, put your head texture on where is shows the head, body on the body, and so on. Poser will figure it all out when you tell it to use the new texture. Forgive me if Abraham told you the same thing, I don't do French!