Instructions
Launch Steam by either double-clicking the icon on your desktop or accessing it through the "Start" menu.
Click "Games" at the top of the Steam window, followed by "Activate a Product on Steam" from the drop-down menu.
Click "Next."
Click "I Agree."
Enter the 25-digit "Modern Warfare 2" CD-Key. This is found on the back of your "Modern Warfare 2" game coupon, included in the HIS 5830 box. Click "Next" after the key is entered to register the game to your Steam account.
Click "Next" to automatically download the game to your computer's hard drive.
Click "Library," followed by "Modern Warfare 2" after installation is complete.
Click "Play" to begin playing "Modern Warfare 2."