Instructions
Select the "PlayStation Network" tab on the main menu of your PlayStation 3.
Select "PlayStation Store."
Select "Add-Ons," located on the left-hand side of the screen.
Select "Disc-Based Add-Ons," followed by "A-L" and "Call of Duty: Black Ops Add-Ons."
Select the DLC pack you wish to purchase from the three listed. As of July 2011, each map pack costs $14.99.
Select "Buy Now" to purchase the map pack, followed by "Download" to download and install the map pack. Once installed, the "Black Ops" DLC maps are automatically added to your map rotation during multiplayer play.