Instructions
Windows Media Player 12
Click on the "Stream" menu located in Windows Media Player 12.
Click on the "Turn One Media Streaming" button.
Click on the "OK" button. Media from your computer will now show on your Xbox 360.
Windows Media Player 11
Right-click on the "Library" tab located in Windows Media Player 11, then click on "Media Sharing."
Click on the "Share My Media" link, then click "OK."
Click "OK" once Xbox 360 appears with a green check mark.
Zune Software
Click on the "Settings" tab in the Zune software.
Click the Xbox 360 icon.
Choose all media types you would like to share and click "OK."