Not sure if it works yet, but if it does, VLC continues to impress as the most useful open source app I've used since GIMP.

From Converting movies to .mp4 with VLC media player:

This page is a simple walkthrough on how to encode almost any movie you have to the .mp4 format (so you can put it on your ipod / cellphone / anything else). The only thing you need for this guide is the AMAZING, FREE, program called VLC media player.

(useful tutorial follows on the page, linked above)