Some one else asked that question on another thread.
It seems you will need the Cerberus code for the DLC.
I wasn't sure what exactly that contained as I bought it last week from new.
I checked the offical ME2 site and they had this to say:
"Activate your Cerberus Network card and receive access to exclusive benefits. Revisit the emotionally stirring Normandy SR-1 crash site, recruit the deadly bounty hunter for hire Zaeed Massani, equip the latest gear and firepower with the Cerberus Assault Armour and Eviscerater Shotgun, and pilot the formidable Hammerhead. With more content and updates coming free to Cerberus Network members, make sure you activate your card inside your copy of Mass Effect 2. Check back often for all the latest info and upcoming content for Mass Effect 2!"
So I think getting the Cerberus code is pretty improtant especially if you want all the DLC.