Instructions
Open "Windows Media Center" from the Windows Mobile phone.
Select "Tasks" in the "Start" menu.
Select "Add Extender." A new screen will pop up; click "Next."
Plug the phone into the Xbox 360 using the USB cable.
Turn on the Xbox and locate "Windows Media Center" from the dashboard. This will automatically begin the adding extender process.
Follow the on-screen instructions until an eight-digit number pops up. Write down this number.
Enter the eight-digit code in Windows Media Center on the computer. Click "Next."
Follow the instructions to complete the process. Click "Finish" on the final page.