How to Find Out Which Maps You Need for Annex

Navigate to the "Game Marketplace" tab on the Xbox 360 main menu.

Select "Explore New Games."

Navigate to the "Titles A-Z" tab and select "G."

Select "Gears of War 2" from the list provided. The list is in alphabetical order.

Select "Extras."

Select "Combustible Multiplayer Map Pack."

Select "Download Now." As of September 2011, this map pack costs 400 Microsoft Points to download. Once the download is complete, the maps are automatically installed and added to your game.

Download the Flashback Multiplayer Map Pack following the same steps as the Combustible Map Pack. As of September 2011, the Flashback downloadable content costs 400 Microsoft Points to download.

Launch "Gears of War 2" and select "Multiplayer" from the main menu.

Select any playlist. While playing, the maps and game modes are voted on by the players. Continue playing until the appropriate map and game-type appears.

Win an Annex match on every map in both map packs. These maps are Flood, Gold Rush, Fuel Station, Gridlock, Subway, Canals, Mansion and Tyro Station. When you win a match on one of these maps in Annex, a pop-up message appears in the lower right corner displaying your current progress toward the achievement, such as 2/8. When you have won a match on every map, the achievement appears at the bottom of the screen.