Sonic and company are back and better than ever in Sonic Adventure 2: Battle for Nintendo GameCube. Dr. Eggman is up to his old tricks, and it's up to Sonic, Tails, and Knuckles to stop him yet again. Sonic Adventure 2: Battle features faster action, all-new two-player games, and a branching storyline that lets you choose to save the world as the Hero side, or conquer it as the Dark side. Two new playable characters enter the Sonic universe — a mysterious dark hedgehog called Shadow, and a jewel-thieving bat named Rouge. In the single-player mode, you'll go through more than 30 unique stages, which include everything from a forgotten pyramid, an abandoned military base, and a giant space station. Then there's the expanded two-player mode, which features 12 playable characters competing in new head-to-head games. All of this adds up to Sonic's biggest adventure yet!Go to: http://store.steampowered.com/ and download STEAM client
Click “Install Steam” (from the upper right corner)
Install and start application, login with your Account name and Password (create one if you don’t have).
Please follow these instructions to activate a new retail purchase on Steam:
Launch Steam and log into your Steam account.
Click the Games Menu.
Choose Activate a Product on Steam…
Follow the onscreen instructions to complete the process.
After successful code verification go to the “MY GAMES” tab and start downloading.