This article describes how to activate Windows XP by using a product key that is different from the one that you used when you installed Windows XP.
You must enter a unique product key when you install Windows XP, or when you activate it. If you install Windows XP on a second computer by using your original CD, and then you purchase a second copy of Windows XP or a second license, you must change the product key before you can activate the product. To modify the product key at the time of activation, follow these steps:
Click Start, point to All Programs, point to Accessories, point to System Tools, and then click Activate Windows.
Click Yes, I want to telephone a customer service representative to activate Windows, and then click Next.
Click Change Product Key, type the new product key, and then click Update.
Click Telephone, and then follow the on-screen instructions to complete the activation process.
Product activation validates that the software product key, or product identification (required as part of product installation), has not been used on more computers than is permitted by the software license. Activations that use the same product key on the same computer are unlimited. Product activation discourages piracy by limiting the number of times that a product key can be activated on different computers.