Accomplish the indicated achievement to get the corresponding number of 
Gamerscore points:

Armored Attack (6 points): Get in the tank with two other players. 
One Man Army (7 points): Kill 200 enemies. 
Veteran (7 points): Complete the game on Black Ops difficulty. 
Mercenary (15 points): Complete the game on Suicide Mission difficulty. 
Humanitarian (10 points): Rescue all of the POWs in the game. 
Sleuth (20 points): Find all of the Secret Areas in the game. 
Brasso (10 points): Achieve the 12X score multiplier. 
Hero (10 points): Achieve the 24X score multiplier. 
Freedom (25 points): Free 25 POWs. 
Madman (30 points): Attain a 24X score multiplier on every level. 
Combined Assault (40 points): Complete the game with at least one other 
player. 
Reckless Driver (20 points): Kill 40 enemies while in a vehicle.