I use MacTheRipper and VisualHub to convert my DVD movies for iTunes / Apple TV use. After VisualHub automagically imports the movie to iTunes, I look up the movie on IMDB.com or MovieGoods.com to find the DVD cover that I like.
Once I find the DVD cover, within iTunes I do a Get Info on the movie, click the Artwork section, and drag the image from Firefox directly to the Artwork section. (You may have to delete what iTunes auto-picked for you.) Then cut/paste the movie's description into the Info » Comments section, so you have the movie's short description. This gives your iTunes / AppleTV movies clean look.
Mac OS X Hints
http://hints.macworld.com/article.php?story=200707070828373