I only have the trial version of flip4mac, and it does work. VisualHub
(http://www.techspansion.com/visualhub/) used to work until an Xbox
update made it so that one had to use WMA as the audio codec in video
files, while VisualHub uses Mp3. It is said that a fix being worked
on, but who knows when that will work out.
So far, there is no easy or cheap way to encode for the Xbox 360, but
solutions do exist.