[-=[XTC]=-Body Bagger]

What entities do you mean, Windows , doors or static models?.
You can re-turn your brushes to strutural by selecting them and clicking make structural.
The ones that u walk through, you texture them with either, wood, metal texture. They are found in the textures/common menu.
If you have static models that you want to turn to detail you have to select them and bring up the entity window and them tick the detail box.
Craig