Microsoft offers the answer to this question here. It applies to earlier versions of Microsoft Office as well.
- 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:
- Right-click the Registration subkey, and then click Export.
- In the Save in list, select a location to save the registration
entries.
- In the File name box, type a name for the .reg file that you want
to export, and then click Save.
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:
- Right-click the DigitalProductID registry entry, click
Delete, and then click Yes.
- Right-click the ProductID registry entry, click Delete, and then
click Yes.
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.
