Instructions
Look on the back of your Fable 2 Collector's Edition package. You will find a code labeled "Exclusive Content Code."
Go to the Xbox Live Marketplace by going to the Xbox Live menu (this will open when you start your Xbox), and choosing the "Marketplace" tab with the "A" button on your controller.
Choose "Enter Code" from the Marketplace options by pressing "A." A box will open.
Type the code into the box using the keyboard on the screen. Use your controller's joysticks to move the arrow to the letter or number you need, and press the "A" button. When you are done, click on the "Done" button. You will find your new energy sword in your character's inventory when you start the game.