In Proe2001 it was possible if you do an external copy or a merge from another part, that you can handle the layertree for the component in the seperate window. Now if it is done in WF4 or Creo2.0 it is not possible to switch on the layertree from the menu in the separated window which is opened, because the menu point is missing.
you have to stop here. Switch to the part, that is copied, manage the layers and then you can go on with merging.
The menu butten layers should be implemented again in the seperated opened window.