1. Click on Start and then Control Panel.
Tip: In a hurry? Type system in the search box after clicking Start. Choose System from the list of results and then skip to Step 4.
2. Click on the System and Maintenance link.
Note: If you're viewing the Classic View of Control Panel, you won't see this link. Simply double-click on the System icon and proceed to Step 4.
3. Click on the System link.
4. In the Windows activation area of the View basic information about your computer window, you'll see the status of your Windows Vista activation and your Product ID number.
Note: The product id is not the same as your product key.
5. Next to this information, you should see a Change product key link. Click on this link to start the process of changing your Windows Vista product key.
6. When the Windows Activation window appears, enter your new product key in the Product Key: text box.
Click Next to continue.
7. Wait on the Activating Windows... message until the progress bar is complete. Windows Vista is communicating with Microsoft to ensure that your product key is valid and to reactivate your Windows Vista installation.
8. The Activation was successful message will appear after your product key has been validated and your copy of Windows Vista has been activated.
9. That's it! Your Windows Vista product key has been changed!
Click Close to close this window. You can now also close the System window.

Why would I need to change the Vista Product Key code?