As far as I know, there is only one "secret" achievement. The other achievements are listed on Xbox.com, the only thing is the player must have a free Xbox LIVE account for his/her player profile before said player can look at the list of achievements.
The secret achievement is the only one that I have unlocked that isn't named in the list of someone who hasn't played the game: "Flight Attendant--kill all five enemies during the zero-gravity scene on 'Turbulence'."
the first one is entering first prestige mode.
the second... no one knows yet...
The related links lists 64 of the achievements / Trophies each with the own detailed link to provide more information
you can find a list of achievements at: http://www.xbox360achievements.org/game/call-of-duty-modern-warfare-2/achievements/ and also a guide for them at:http://www.xbox360achievements.org/game/call-of-duty-modern-warfare-2/guide/
The Call of Duty 4 Achievements for Xbox 360 can be found here: http://www.xbox360achievements.org/game/call-of-duty-4-modern-warfare/achievements/
Over time, you get achievements when you collect enough.
Nothing really, they just unlock achievements.
You have to achieve them xD (Most of them include the single player campaign)
nothing you just get achievements but infinity ward said that they will do what they did on cod 4 modern warfare 1 and make cheats for when u collect them
well call of duty and modern warfare are the same it is called Call of Duty: Modern warfare and then came call of duty: modern warfare 2
Call of Duty 4: Modern Warfare came out first. This is the first game in the Modern Warfare series, and Modern Warfare 3 is the third game in the Modern Warfare series.
Call of Duty Modern Warfare came before Call of Duty Modern Warfare 2
The related link lists and describes the 51 trophies for Call of Duty Modern Warfare 2 The 50 achievements for the Xbox 360 Game and the points earned are also included in the descriptions at the related link
no theres a call of duty modern of warefare 2
"Call of Duty 6" "MW2" "Modern Warfare"