Shot in the dark here.....what resolution are you outputting through HDMI? If it's something like 720/1080 the source component (i.e. DVD player) may be doing the scaling as opposed to the TV. Stick it on it's lowest resolution and then try.
I am using a HD digital cable modem. Which is outputting 1080.
I need this because some of the channels like HD1 offer this resolution.
The drawback is that some of the channels are 4:3 ratio and broadcasting 16:9 material in such a way that you need zoom mode to fill the screen and have proper aspect.
Now I end up with two options. Have an image that is strechted and has blackbars top and bottum (very ugly) or have a small picture in the center with bars all around.