An update is scheduled to hit Gears of War 2 this month, and with it comes a new set of achievements tied to the multiplayer map packs Flashback and Combustible. Microsoft has released details on an additional seven Gears 2 achievements ahead of the patch's release (via X3F).
In addition to adding a potential 175 extra gamerscore to the Gears 2 experience, the patch will also address a multitude of online multiplayer issues, which you can read about in detail here. Here's a full breakdown of each upcoming achievement, as described on Xbox.com:
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12:00 am PST January 20, 2009