Battlefield Bad Company 2 Vietnam is not a stand alone download,  To activate the product you use your activation code to install via Battlefield Bad Company 2's main menu. 

  1. Open Battlefield Bad Company 2 
  2. Make sure your game is patched. 
  3. Use the drop down menu "Battlefield Bad Company 2" and choose Vietnam 
  4. A box will pop up and you put your activation key in and press Redeem Code. 

Once you redeem your code in this menu you should be good to go!