Achievements are unlocked by accomplishing the listed task and will give you the listed number of gamer points. If you have an X-Box 360 gamertag, you can log in using this same gamertag and the gamerpoints/achievements will count the same as if you were playing the 360 version / any other X-Box 360 game.

Achievement	How to unlock
Aiding the Outcasts ( 20 points )	Completed "Aiding the Outcasts"
Operation: Anchorage ( 40 points )	Completed "Operation: Anchorage"
Paving the Way ( 20 points )	Completed "Paving the Way"
The Guns of Anchorage ( 20 points )	Completed "The Guns of Anchorage"