Instructions
Download the "Bring Down the Sky" content pack via Xbox Live or the Bioware website. As of 2011, this pack is priced at 400 MS points.
Start the "Mass Effect" game. Select either a current game file or start a new game.
Play the game until you are given access to the Galaxy Map on the Normandy. Save the game and quit to the main menu.
Select "Extras" and then select "Downloadable Content." Highlight and select "Bring Down the Sky."
Load the saved game where you have access to the Galaxy Map. Get on board the Normandy if you are not there already.
Pull up the Galaxy Map and select the newly available Asgard System, located south of Noveria. Select Asteroid X57 as your landing point to start playing the mission.