GardenRN,
First, call me Eric.

Have you posted pictures of your greenhouse project? I'd like to see it.
I purchased 11 storm windows from a consignment shop for $35.00. The front of the greenhouse ( south) has 6 windows and the east / west 2 each. All parts of the walls without glass are insulated. Ridged insulation. What's nice about storm windows is 2 screws and the window comes out of the frame. Its a frame within a frame. Ease of ventilation. Roof is made from sliding glass doors. This is tempered glass. Much safer overhead.
[img]https://i67.photobucket.com/albums/h300/eric_wa/Greenhouse%20May%2026%202010/DSC02216.jpg[/img]
[img]https://i67.photobucket.com/albums/h300/eric_wa/Greenhouse%20Photos/DSC01957.jpg[/img]
Eric