When you install or activate Windows XP, you must use a unique product key. If you use the original Windows XP CD-ROM to install Windows XP on a second computer, you must change the product key before you active the product:
1. Start / All Programs / Accessories / System Tools / Activate Windows.
2. Press Yes, I want to telephone a customer service representative to activate Windows and press Next.
3. Press Change Product Key and type the new product key.
4. Press Update.
5. Press Telephone and follow the on-screen instructions.
NOTE: See Description of Microsoft Product Activation.