I added a dvd video which was sitting in my computer disc tray to the Arranger but the video is very "skinny" in the Preview Monitor. The audio came out fine.
By 'skinny' do you mean the image is squashed in from the sides with probably black bars to the left and to the right? This would be due to a mis-match between the 'aspect ratio' of your project and that of the imported DVD. First, is you project ('File' >>'Settings...' >> 'Movie' or [E] key shortcut) what you want -- 4:3 traditional TV shape or 16:9 wide screen? Then check with a right click on your clip and go to 'Properties', usually at the bottom of the menu. Changing the aspect ratio from 4:3 to 16:9 may fix the problem.