I just messed around with this for a few minutes. How I got it to work was :
1. Open windows media center on pc
2. Turn on 360, push the windows circle on the middle of the remote and to to the tab that has media center on it. Open it, you will get a code for setup after a step or two
3. Get the code and go to pc
4. Go to extenders on the pc media center and enter the code
5. It should be set up now
Then go to your phone > all share and let it do its thing. Select the appropriate option and play list items then select xbox 360 media center and it should play.
I played some mp3's without issue. I didn't try any video yet.
Note 2 (AT&T) and Nexus 10
Treo 650 - PPC 6600 - iPhone 2G - IPhone 3G - HTC Hero - EVO - Palm Pre - Epic 4g - HTC Inspire - Galaxy Nexus - Galaxy S 3