Microsoft Product Activation which will only allow you to install Windows XP on one system at a time. Under this new policy, you must use the CD Key code that comes with the software to install the operating system. You’ll then have 30 days in which to contact Microsoft, either via the Internet or by telephone, and activate the software. This will help them to reduce the software piracy.

When you do, you won’t have to give Microsoft any personal information, just your CD Key code. Microsoft will assign you an activation code, which you’ll then enter in the appropriate text box in the Microsoft Product Activation wizard. If you don’t activate the software within the 30-day period, you won’t be able to boot Windows XP past a dialog box that prompts you to enter activation code.