Instructions
Power on the Xbox 360 and sign into a gamer account.
Navigate to the "Games Marketplace" tab of the Xbox dashboard and go to "Game Add-ons" and press "A" on the controller.
Cycle to "Titles A-Z," and press "A."
Highlight "B" from the listed alphabet and press "A" on the controller.
Navigate to "Borderlands" on the listed games and press "A."
Select the DLC you want to download and press "A."
Confirm the DLC purchase or add more Microsoft points to your account when prompted.
Choose "Download Now" from the listed options to download the chosen DLC packs. The DLC will download and install automatically to your hard drive, modifying your game content.