I think you should try Origin now...

[chawlie fair]

So, I recently read on PC gamer that you can Activate Steam game keys on EA's Origin download majiggy, so I downloaded origin and decided to try it myself, since I'm planning to download BF3 anyway. I redeemed my Bad Company 2 code on Origin, and it gave me two different games to choose from: regular Bad Company 2 or Bad Company 2 Ultimate Edition, which has all the DLC

Now i haven't downloaded the actual game through origin yet, so it might not let me play the Vietnam pack, but if it does,I can tell all my friends that I'm a l33t hack3r.
Has anybody had this happen? Does it work with other games?

 

[ChickenZombie]

I'm trying right now! God I hope this works

 

[Roald Groenen]

Most games (those released after 2008) can be redeemed in Origin after buying them through Steam. You will be able to access Vietnam as usual as it is linked to your EA account with entitlements.

Edit:

To be more specific the game is already linked to your account the moment you log in to EA servers and use your code. Redeeming the code simply adds a second entitlement that allows you to download through Origin.

 

[Comando96]

and it gave me two different games to choose from: regular Bad Company 2 or Bad Company 2 Ultimate Edition, which has all the DLC

Mass Effect 2.

Does anyone know if that'll have all free DLC too? If so I'll jump on ship in order to get the DLC before this ship sinks when steam rams into it.

 

[Roald Groenen]

Same thing:

Your DLC is already linked to your EA account and can be downloaded again via http://social.bioware.com under Profile -> My registered content.