ok, here a few things to try. first off, when you install WMP11 it gets rid of media connect and intergrates it into MP. to check on this in WMP11, click the down arrow under library, then go to media sharing. check to make sure sharing is enabled, and the 360 is showing up and there is a green check mark beside it. then click the sharing button and make sure music, pictures, and video is check (or check only what you wan tot share. ) make sure the star ratings are what you want along with parental ratings. click ok.
to be on the safe side, go to the settings blade, then computers on the 360. go to the windows computer (not the media center computer) and dissconnect it to be on the safe side.
now, go to the media blade, then music, click yes you d/led the software, and see if your computer shows up. if not, turn off your firewall. if you are using windows firewall, go to the controll panel, then security center, and turn it off. if you have another type of firewall, you'll have to find out how to dissable it. now try it, if it works, then this is your issue.
i'm not sure right now what ports you need to open, if this fixes any of your problems, hit me back with a reply, and i'll look it up. I use windows one care live, and it blocks this on my computer... now the ver 1.5 beta also blocks it, but it has a nice little wizard that will open them for you, but they are still closed by default.
let me know if this helps.