I had the same problem - ask TVC 15. I couldn't figure out the problem. I think it takes a couple of fresh reboots with the network and the PC/360 to get it all working for some odd reason. Now that I've got my PC, 360 and Zune working in harmony, it's like sex.
I'll stream Dexter to my living room, hook up an unlistened to PTi podcast and listen to that while playing CoD4, charge my Zune, setup 360 playlists. It's great.