The windows are just JPG textures loaded with the alpha flag (black=transparent, white=opaque). Of course, if you use a file format that supports alpha (TGA or PNG), the alpha information in the texture will be used instead of the color map.
Oh! And this map is not finished yet. It's author sent me a nearly finished version two days ago, and it is looking really impressive :D
Oh! And this map is not finished yet. It's author sent me a nearly finished version two days ago, and it is looking really impressive :D