Or you could try this...
in your 3D app, Build a frame with the center open. Make it the same size as a standard floor segment.
Then make a second mesh for the "Glass". Export the glass by itself, and use Entity workshop or simalar, to create the glass entity ( with texture that includes a 50% gray alpha channel for transparency). Place the entity files in the Entitybank folder in the segment creator directory (include the .fpe).
Import the frame mesh (with texture)using the "mesh" button.
Then import the entity (.fpe), and position it inside the frame.
Save the segment. You can even make it breakable. You can also replace the window with an animated door entity, swinging or sliding open, and closed as well. No CSG punch needed.
Done!
hope this helps.
2.5ghz QuadCore,4gb ram,1gb ATI graphics. Dual OS. WinXP, Win7.