Transparent Windows

Objects 1 and 2 are two halves of the same window (see the screenshot on my site).
They can be set to open like double doors. Don't forget to uncheck 'blocks vision' 
from the Door > Rotating property.

Object 3 is a smaller version. I'm not sure if I used it in my FM but the model's there anyway.

Extract the files to your obj folder.

The texture is from a picture I took of a window at Caernarfon Castle in Wales.

R Soul