BGLcomp SDK re: textureIndex.......? What?

Hi,I thought I posted this question or as I need help but I don't see it in the forum.I am making buildings per the SDK and have printed copies of the "texture number" .bmp they refer to. I also have been playing with the textureIndex... values. I have some luck with this but am puzzled. The eamples and ny experiments show I can be outside of the .bmp's bounds of 128x128 in selected cases and still get parts of that texture .bmp. Can anyone out there give a desription of how these indexes are used? I thought I knew but I guess not! How come the windosw textureIndexe's have x,y,z and the others only x,z ?Is there any way to control which sides of the building gets some of the texture bmp its pointed to?Larry Costa