If you have the DLC Onslaught for Battlefield: Bad Company 2, try following along with this video walkthrough to see how to beat the Valparaiso map on the Onslaught Co-Op Mode. And you're not going to learn just how to beat Valparaiso on Onslaught, but you're going to see how to win on Hardcore Difficulty. It might be a good idea for you to complete Hardcore Difficulty with a full squad of 4 players: 2 Engineers, 1 Assault, and 1 Medic.
* This guide is for the PlayStation 3 (PS3), but could also be used for the Xbox 360.
Check out some other maps on Onslaught Co-Op mode, Hardcore Difficulty: