Have you looked at the settings on your dvd player and the TV? You normally need to select the option to show 4:3 content in it's native form from both sources, on my 40W5500 this means going into the screen menu and selecting 4:3 in the 4:3 Default setting. As for your dvd player i have no idea as you dont list your player but when i select those options on the TV you can then use the button on the remote for aspect ratio (top middle button on the remote) to change between 14:9, 4:3, Wide etc.
Hope that helps, if not provide details of the dvd player in question and will try to help further.