The Windows Media Player that comes with PocketPCs is not particularly good. Betaplayer is a great, small, free alternative that will play DivX and XviD movies.

Modern handheld computers are perfectly capable of storing and playing even fairly large video files. But if you wanted to watch a whole movie on your PocketPC, it would have to be compressed, and the in-built Windows Media Player is not very good at dealing with compressed files. So in steps Betaplayer, which can deal easily with all sorts of files. You can even add plug-ins so that it will play Musepack (*.mpc) and AAC files, among others, as well.