This is a problem I've had for the longest time, and I just figured it out, so I'm posting here for anyone else that has issues getting ushare and their xbox 360 working together nicely.
You'll need to open not just port 49200 (and verify uShare is running on 49200, as if something is already taking 49200, ushare will increment up to 49201) but ALSO port 1900, which is something called SSDP.
I haven't done any research into SSDP yet, just wanted to post this information on the web for anyone else that may get stuck. I got tired of having to drop all my firewalls to stream my media to my Xbox360.