Texturing a complete untextured 3d model in Bryce 5.5

I have quite a variety of motorcar 3d models but they are all untextured (appear in gray only). When I ungroup the objects to start texturing the parts ... the wheels is one layer and the car body separate. But I want to texture the windows with glass effect and the metal parts with a metal finish. But there is one problem ... one can not ungroup the car body into parts. When I choose a metal finish, the whole body change into the choice I pick including the windows!!

How can I texture the windows on its own or any other parts if the whole body is one group only? Some other models I have this is possible as every part of the whole car is ungroupable. But in this case one can not do it ... unless there is another way!?

Any help will be most appreciated.

Thanks,
Laura