For those Xbox 360 owners who didn't also have an XP Media Center box, DivX streaming from programs like Transcode 360 were always a far reach. Now with TVersity, you can perform on the fly WMV transcoding and streaming from any XP machine.
All you have to do is install TVersity, set up the videos you want to share, and brows to your videos folder on your 360. You should see all the shared videos via TVersity, plus the "online videos", provided you have the right directshow filters. If you're looking for an all-in-one solution, check out the Helios H4000.