When you play the game for the first time steam will provide 1 key for you to type in to activate the game, however there is a second key which is not shown (afaik) which is required to let you obtain the limited edition unlocks and day 1 dlc,
to find the second key you need to quit the game, go to your games section in steam, right click on Battlefield: Bad Company 2 and select "View game CD Key" there you need to make a note of the second key in the list as you simply cannot copy and paste it into the game,
you then need to paste the code in the store to obtain your limited edition unlocks and day 1 dlc.
Extra FYI: you may need to restart steam to receive your promo key, also once you activate it, many people say it takes time before the unlocks actually make it into your weapons and gadgets slots, so don't go raging straight away




















