For video, doesn't the XBox360 only support WMV?
Not to turn this into an xbox360 thread - but the 360's built in "media center extender" feature will support WMV (up to 1080p), MPEG1, MPEG2 (up to firstname.lastname@example.orgMbit/sec), and DVR-MS (MCE's TV-recording format).
But of course this will all only work if you have an MCE computer running somewhere to be the "master" to the xbox360's "slave". Unlike the Roku, which only requires a NAS or other file share.
The 360 will also function as a UPnP client if you have an appropriate server like Windows Media Connect - but apparently only for photos & audio, not video. I can't remember if Roku ever got UPnP working properly on the HD1000, and don't really care....
And finally, the 360 won't be able to play DVDs remotely, only thru the local DVD drive. Since it does support remote MPEG2, I assume this means 1) no remote playback of *encrypted* DVD files, and 2) no menus or other DVD-interactivity when playing remote files.
Most of this info is from here