Keep in mind that I have no experience with the Visio brand of television, but I have a feeling that it is trying to automatically scale your non-hd or non-widescreen images, and you are trying to compensate for it by zooming in on the picture.
You shouldn't need to do this at all.
I would 'assume' that a 42" tv would be 1080p, but I've been wrong before, and it very well could only be 720p - especially if its an older model.
You have to keep in mind that there are (essentially) four TV modes in mainstream use today:
1> Standard definition
2> 420p/i
3> 720p/i
4> 1080p/i
Modes 1 and 2 are for the vast majority of the time NOT widescreen whereas 3 and 4 ARE widescreen. When a non-widescreen picture is displayed on a widescreen display, one of two things can happen. The picture can appear as a more 'square' image with black bars on each side... OR the picture can be stretched out horizontally to fit the whole screen which would make everything a tad bit wider. Faces and bodies look 'heavier' and circles look more like wide ovals.
Modes 3 and 4 are widescreen, but require you to receive a high definition signal, otherwise the TV will simply 'upconvert' a lower resolution onto a higher resolution display. Depending on the methods used by the specific hardware, this can sometimes look quite poor.
Sometimes on hi-def broadcasts, the TV/Cable channel itself will simply upconvert a low-def signal into the hi-def broadcast so that your TV actually receives a hi-def transmission even though it's 'technically' a low-def picture. While the quality of the upconversion is usually better during this process (as opposed to your TV doing the conversion), it still can sometimes be difficult to tell what's going on in the background. You might be able to press an 'info' button that will display the resolution of the broadcast on the screen, and if it is already 720p/i or 1080p/i then there isn't much you can do except to turn off any zoom or override settings you may have enabled.
The best advice I can give is to quit trying to manually manipulate any images on the display. 'Zooming in' isn't going to increase the picture quality (and can actually make it worse). Some shows and commercials were made before the widescreen format was available and in this case you're best off leaving the black border on each side of the picture. If you aren't receiving a Hi-def signal, then you are most likely getting a non widescreen low def signal and you're either going to have to deal with the black borders... or you're going to have to deal with a horizontally stretched out image.
If you do subscribe to a hi-def signal (or are receiving HD broadcasting) then you're going to need to concede to the fact that some shows, movies and commercials are simply going to have these borders. While you can manipulate the settings to help out with this somewhat, you're constantly going to be changing things everytime a 'cropped' show comes on versus one that is natively widescreen. It's much easier to simply get used to the cropping for now. I don't even notice it anymore. (As time passes and the technology progresses you'll find this to happen less and less).
My in-laws use low-def DirecTV with a hi-def widescreen television. They have it set to stretch out the image and have gotten so used to it that when they come over and see the hi-def picture on my TV they swear up and down that my picture is 'squished' and it is that exact reason they don't want to upgrade to hi-definition. I can't convince them otherwise so whatever.. as long as they are happy, right?
As for your 'just scan' setting, my guess is that it tells the TV not to manipulate the image any... but only to display it as it is received?
Here's a little graphic I made to help a squaddie out with understanding the whole aspect ratio/definition thing. Also read my graphics guide
HERE as it will teach you a lot too.
