ZZk is partially correct.
You would need to get your xbox 360 jtagged which will allow you to run games of the hdd, download free dlc aswell as download full xbla live games+ way more. But the only way to run the jtag hack you would need a dash that is 7371 or lower.
to check your dashboard version turn on your console, go to system settings > console settings > system info and check under "currernt dash". If its hackable i reccomend you dont update your dash.
check out for more info
http://gmodz.ca/content.php?content_id=8&sub_menu_id=23