Harish Answers: How to change the product key for Office XP, for Office 2003, and for the 2007 Office system

You cannot change the product key for Microsoft Office XP, for Microsoft Office 2003, or for the 2007 Microsoft Office system without first removing and then reinstalling Microsoft Office.

To resolve this issue, follow the steps in this section.

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 (http://support.microsoft.com/kb/322756/ ) How to back up and restore the registry in Windows

Note If you try to open any Office programs after you complete the steps, you receive a message that prompts you for a valid product key. Make sure that you have a valid product key before you start these steps.

Close all Office programs.
Click Start, click Run, type regedit, and then click OK.
Locate and then click the following subkey, depending on your version of Windows and of Office:
32-bit versions
2007 Office system
HKEY_LOCAL_MACHINE \Software\Microsoft\Office\12.0\Registration
Office 2003
HKEY_LOCAL_MACHINE \Software\Microsoft\Office\11.0\Registration
Office XP
HKEY_LOCAL_MACHINE \Software\Microsoft\Office\10.0\Registration
64-bit versions
2007 Office system
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Office\12.0\Registration
Office 2003
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Office\11.0\Registration
Office XP
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Office\10.0\Registration
Export the Registration subkey.
You can make a backup of the values under the Registration subkey if the new product key does not work. To do this, follow these steps:
1. Right-click the Registration subkey, and then click Export.
2. In the Save in list, select a location to save the registration entries.
3. In the File name box, type a name for the .reg file that you want to export, and then click Save.
Note In steps 4a through 4c, you created a backup of the Registration subkey. You can restore the Registry settings of the Registration subkey by double-clicking the .reg file that you saved in step 4c. The contents of the .reg file are automatically exported to the Registry.
Under the Registration subkey, there may be several Globally Unique Identifiers (GUID) that contain a combination of alphanumeric characters. Each GUID is specific to a program that is installed on your computer.
Click a GUID. Then, view the version of Office that is listed in the right pane for the Productname registry entry. After you find the GUID that contains the version of your Office program, follow these steps:
1. Right-click the DigitalProductID registry entry, click Delete, and then click Yes.
2. Right-click the ProductID registry entry, click Delete, and then click Yes.
  For more information about how to identify the correct GUID for the version of the Office suite or program that you have installed on your computer, click the following article numbers to view the articles in the Microsoft Knowledge Base:
  928516 (http://support.microsoft.com/kb/928516/ ) Description of the numbering scheme for product code GUIDs in 2007 Office suites and programs
  832672 (http://support.microsoft.com/kb/832672/ ) Description of numbering scheme for product code GUIDs in Office 2003
  302663 (http://support.microsoft.com/kb/302663/ ) Description of the numbering scheme for product code GUIDs for Office XP programs
Close Registry Editor.
Open an Office program, such as Microsoft Word. When you receive a message that prompts you for the product key, type the correct product key, and then click OK.