If the film you're watching on your laptop is too wide to fit, and you want to zoom in on the movie in DVD Player, there's a nice slider for it in menu Window » Video Zoom. In QuickTime Player, however, there's only an option to completely zoom in, cutting out a lot of the movie on both sides. So if you want a compromise between those two views, do it this way:
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090517134916698