How can I insulate a immense pane pane? I have a voluminous window (approx 12' x 8') within one room...

I have a voluminous window (approx 12' x 8') within one room and it gets amazingly drafty now that it's cold outside. The frame around the pane is metal and I don't want to compromise the opulent since it's a focal point of the room.
I own an 18' x 4' above ground...
Answers:    3M Company 2141 62 x 210 Indoor Window Insulation Kit
http://www.epinions.com/content_78899809...
http://www.amazon.com/3M-Company-2141-In...
stuff works great easy to see through cartridge comes of easy after use can be reused if it will still fit an another fanlight
Two sides of a modular home not even,...
Sort of expensive but you could have a lexan or acrylic sheet fabricated contained by a frame that would attach into the window return inside. the upper air space would give a clothed insulating effect. the bigger the air space the better the insulating effect.