How to Setup a Xbox 360 for HDMI?

The Xbox 360 HDMI Cable , included with the Xbox 360 Elite system or sold separately, enables a single cable to deliver HD video (up to 1080p) and multichannel surround sound to a TV or an audio/video surround receiver.

Connect to a High-Definition TV

The Xbox 360 HDMI Cable gives you the option of using a single digital AV cable to connect to a high-definition TV.

The Xbox 360 console and HDMI cable work with high-definition televisions including big-screen projection, plasma, DLP, and LCD TVs.

To connect your Xbox 360 console to your high-definition TV (HDTV):

1. Turn off your console.
2. If another AV cable (such as the component HD AV cable) is already connected to the AV port on your console, disconnect it before continuing.
3. Connect the HDMI AV cable connector to the HDMI AV port (not the standard AV port) on the console.
4. Connect the other end of the HDMI AV cable to the HDMI input on your TV.
5. Turn on your console. From My Xbox, System Settings, select the appropriate high definition video setting for your TV.

Reference:http://support.xbox.com/support/en/us/xbox360/hardware/accessories/av/hdmicable.aspx