Buying a cod4 Key

Im looking for a cheap Cod4 key, im very new to steam joined tonight, idk if i need the cd to play cod or not.

Could i have that information relevant to buying the key.

You will recieve your payment once i have cod4 activated on my steam acc.
i am a 5$ donator ( nothing much ) and have 25+ vouches.

My msn is : [email protected]