The new Media Sharing feature of Windows Media Player 11 lets you enjoy the contents of your Windows Media Player library from anywhere in your home. If you have a home network (wired or wireless), you can use Windows Media Player 11 to stream the contents of your library to networked devices. For example, if you have an Xbox 360 or other digital media receiver (DMR), you can use Windows Media Player to stream music and pictures from your computer to that device. This even works with music that you've downloaded from online music stores and services.

Source: Microsoft