Use the following Scripts to force Office to pop-up a wizard for replacing your serial.
you can use this method to fix the the Office Genuine Update warnings by replacing the bad serial with a new genuine one.
Close all running Office Applications, Download and run the script.
Office 2003: ReplaceOfficeSerial2003
Office 2007: ReplaceOfficeSerial2007
Afterwards, open an Office application, like word, and a wizard will come-up asking for a serial.
Note: you can use this method manually for different products from the Office family (like Visio, Publisher etc.) just open RegEdit and goto:
then delete the "DigitalProductID" and the "ProductID" values.
It works like magic!