Dungeon Siege combines the immersive elements of a role-playing game with over-the-top intensity and non-stop action. Dungeon Siege plunges you into a continuous 3D fantasy world where you face off against an army of evil that has been unleashed.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.