Instructions
Windows Media Player 11
Click the "Library" tab located in the Windows Media Player main menu.
Click "Media Sharing" in the "Library" menu.
Select "Xbox 360" in the "Share my media to" box and click the "Allow" button. This will allow you to share media between your Xbox 360 and WIndows Media Player.
Once media sharing is allowed, you can access the media files on your Xbox 360 through Windows Media Player in the "Library" menu.
Windows Media Player 12
Click the "Stream" button located in the Windows Media Player 12 main menu.
Choose "Turn on media streaming" by clicking on it. This will bring up the "Show devices" submenu.
Turn the "Show devices on" to "All Networks."
Click the Xbox 360 icon to highlight it, then click the green "Allow" button. This will allow you to share media between your Xbox 360 and Windows Media Player 12.
Once media sharing is allowed, you can access the media files on your Xbox 360 through Windows Media Player in the "Library" menu.