Harold,

In step 3 of the procedure for importing furniture you can define whether your model is a door or window. This means that when a door or window is inserted into a wall, the walls makes an opening that fits the object. If you need just a hole in the wall, you could use an invisible box, or a hatch from the 3D models page.

Maybe it's a good idea to read the User's guide and use the Help pages of the program.

Hans