The construction for round windows was found in this folder:
http://www.brickshelf.com/cgi-bin/gallery.cgi?f=114824 (hanibal).
Playing around with these round windows,
I came up with the idea of using a Turntable 2 x 2 Plate, Base 
(3680) that makes a perfect frame for the round window.
Now the top is removed from teh turntable,
there is exactly space for 4 trans plates 1x1 (round or square)
to suggest a stained glass window.
Nice side-effect is that the total is not thicker than 2 bricks.

I don't know if anyoen ever has come up with this idea of making
a round framed window. Sure I like to take credits for this idea,
but let me know if there has been someone else who has to be credited :-)

Please feel free to use this ideas in any kind of your mocs
and please let me know what you think.

Daan Bargerbos