On your television (not the wii) there will be a setting for zoom and picture, most likely on your remote. You will want to be displaying in "normal" or "16:9" (depending on the terminology your HTDV manufacturer uses).
Its difficult to say from your description, but its possible you are running in stretch or zoom mode. Changing the aspect should correct your issue.
"Aspect" is usually used when describing an images "aspect ratio", or the lenth by the height of the image. So a 16:9 TV will have a 16:9 aspect ratio. On my remote, the button that changes the aspect is called "P.Size" (I have a Samsung HDTV). My options are 4:3, 16:9, Zoom1, and Zoom2. Your TV might have those, or might have ones like "Normal", "Stretch", or other names.
I have the React component cables, and I have a Samsung 56" DLP HDTV. The picture quality is much better than with the composite cables, colors are brighter and the picture is more crisp.
