I'm not a Mac user, so I can't give specific advice.
But in general, to fix what you describe will require a video editing program that can change the horizontal size. There are several for PC's. Don't know what's available for Macs.
To make DVD WS to FS again requires a good video editor program for best results. The simple way, to just magnify until full screen, will usually result in cutting out important side parts of some scenes. The movie studios zoom and pan while making a film copy to keep the important parts in view, an expensive proposition. Of course, digital video editing is much faster and cheaper.
Fav quote - "Experience is whatcha don't get 'till ya don't need it no more."
System - Athlon 1.4GHz, Win98, Hauppauge PVR250 receiver and compressor.
Software -Magix Movie Edit Pro 10, Nero 6 + NeroVision Express, Moho 4.61, PSP 8.1, Bryce, Quicktime 6.52 pro, Goldwave 5, DVD-Lab.
Cameras - Panasonic GS9, Canon ES8400V, Canon EOS D20 and Canon A70