Are you trying to take a 'dumb' TFT monitor (say widescreen 16:9) and have it take the incoming signal (perhaps 4:3 aspect ratio) and duplicate the image on a the left and right halves?
For example:
Ratio W H Aspect Ratio expressed
16:9 1920 X 1080 1.777777777777778
4:3 640 X 480 1.333333333333333
If you were to split a 1920 X 1080 monitor and split it vertically down the middle you would wind up with something like 960 X 1080 (AR 0.8889) - you could expand a SD image out to fill that but it would be both stretched and chopped.
