for the DVD issue you have 3 choices
as it is
black bars top and bottom (i.e. showing widescreen on a normal TV)
everything looking like it's been squashed and looking thin (forcing a widescreen film into a normal aspect ratio)
if you use a player like VLC player to play your DVDs you can right click on video when it's playing and there is a setting to force aspect ratio so you can see which of the above 3 you prefer.
http://www.videolan.org/vlc/
For the Xbox I can't really say because you've not mentioned if it's a old style CRT TV or a new flat screen TV (model number would help)