Instructions
Configure Windows Media Center on your PC. If your PC already has Windows Media Center installed, click the "Windows Media Center" button in the Start menu and follow the onscreen directions to configure the program. Visit the Windows Media Center homepage if you do not have Windows Media Center or are unsure whether or not it is installed on your computer (see Resources for link).
Connect the Xbox 360 game system and the PC to the same network.
Highlight "My Xbox" in the Xbox 360 menu. Highlight "Windows Media Center" and press the "A" button.
Copy down the 8-digit setup key that is displayed on the TV screen.
Click on "Tasks" in the Windows Media Center menu on your PC. Click "Add Extender." Enter the setup key obtained in step 4.
Highlight "Windows Media Center" in the Xbox 360 menu and press the "A" button. Use the control pad to navigate the Media Center menu and highlight music tracks, movies or television episodes you wish to stream. Press the "A" button to select a media file and stream it to your Xbox.