MS Office 12.0.1 Update Rejected

I have Office: Mac 2008 Home & Student Edition (12.0.1) installed with
the application located in the applications folder.

When I select to install MS Office 12.0.1 Update, I am presented with
the following message:

You cannot install Microsoft Office 2008 for Mac 12.0.1 Update on this
volume. A version of the software required to install this update was
not found on this volume.

Is this because I have not purchased the "professional" edition of
Office?