Re: CAN\'T INSTALL!
Most of the time, this means that you have a dirty lens in your DVD drive. To verify, you can try installing the game on a friend's machine.
However, you can still install the game without using your DVD. Open the Steam client (which gets installed first), create your Steam account, and on the Games list, open the Games menu and click "Activate a product on Steam..."
Enter your CD key when prompted (it's located on the Quick Reference card that came with the game), and the game will download over Steam.