I don't know anything about the "set up room" as Poser 4 does not have one (I use a text editor or CR2Builder), but there is no problem with using props in this situation. The main point in making a door is to move the origen of the door prop to to lign up with the door hinge, do this before translating the door or parenting it to the figure. This can be done in the Poser interface, select the prop, then from the menu bar do; Object>Properties>Display Origen, new dials will appear in the paramitrs pallet, and cross hairs on the prop, align the origen, test the yRot, then hide the origen again.