Why is my Windows Media Center unable to hook up to my Xbox 360?

I have been trying ALL DAY to connect my Xbox 360 (my step-brother's old fat one) to my PC for the Windows Media Center, but every time I try something happens. I've tried everything from clearing out my registry, enabling ports, even shutting down my firewall, and still NOTHING is working! I've been putting in the 8-digit code for the extender, but every time I try, I always get an error message! Does anyone out there have any ideas?!