Hi, I don't know how to set scaling to maintain an aspect ratio such as 4:3. The method of lowering your resolution to something that isn't native and then selecting the now selectable option to maintain aspect ration doesn't work. Whenever I set the resolution back to it's native res it move back to the default scaling option. BTW I have a HD5850 and I'm running catalyst 10.11.
More aboutmaintain aspect ratio
Have you looked at your monitor options? A lot of monitors allow you to stretch the image or not.