There is no such thing as a 4:3 broadcast on a HD channel. I know you are looking at a 4:3 commercial on your HD channel and thinking to yourself "This guy doesn't know what he's talking about."
Really - I do.
When you see 4:3 programming on a HD channel they are actually broadcasting a full 16:9 HD broadcast. They take the original standard definition 4:3 information, then they put black bars on the sides, then they convert it to 1080i or 720p format, then they broadcast it. So, you actually get a full 16:9 broadcast in 1080i or 720p. Which, most TVs can't manipulate at all.
But, quite often, as said above, the cable box, or satellite box, can still stretch, zoom, etc. with the HD image. But, it is all TV and box dependent. If your TV won't do it, then check to see if the cable/sat box will do it. If neither will, and it is a long show, then switch to the regular definition channel and watch that way. At least until you have your display properly broken in.
I know with my display, the TV does not allow manipulation of HD signals, but the cable box does, so I use the cable boxes aspect controls.
