Windows Media Center on XBox 360 PLEASE HELP!

First let me congratulate Microsoft for messing up again.

Okay, so this is ticking me off. I have a HP Desktop with Windows Vista Home Premium so I don’t need to download extra software so they say. My Desktop is connected to our network router with a Ethernet Cord, and my XBox 360 Elite is connected to the **SAME EXACT NETWORK **wirelessly. I have disabled my Windows FireWall completely because it keeps saying “Make sure your firewall is set up to allow UPnP discovery.” I have Norton Anti-Virus which doesn’t come with a Fire-Wall. I go to Windows Media Center, go to tasks, then Add Extender. I enter my 8 digit code that I was giving from my XBox 360. It “Configures Computer Settings” but then it says: “Extender not Found, make sure your firewall is set up to allow UPnP discovery.” I already had it enabled. I have also tried having my Computer and 360 wired into the network but my computer doesn’t detect my 360 and my 360 doesn’t detect my PC. If you have any more question just email them to me don’t ask them in your answer please. Microsoft, you’ve really outdone yourself here. I’ve never found anything simple when it comes to you. I love you Microsoft but you make me mad sometimes. You cannot expect everyone to be a tech guru. I wish I was, believe me I do because I love computers and learning more about them but I’m not a tech genius yet. Please I’m begging you to help me. Email: Benbojojo@yahoo.com