Hi, I justed want to share with everyone what I did to stream pretty much any format to my Xbox.
Very simple, all you need is a Twonky server (http://www.twonkyvision.de/) installed as a service. You need to log in using remote desktop to install it, but after that, everything's straight forward. I also installed Juice (http://juicereceiver.sourceforge.net/) as a service to pull down podcasts. This combination pulls down all my video podcasts in HD H.264 and streams them perfectly.
Good luck,
Dan