I meni se to desilo kad sam instalirao novi Office (uz postojeći). Na u članku http://support.microsoft.com/kb/928091 kažu sledeće:
Windows Installer messages in Word
If you have multiple versions of Word installed on the computer, the Windows Installer may start when you start Microsoft Office Word 2007. And, a message that states that Windows Installer is preparing to install Word may be displayed. You may receive this message before Word starts.

The Windows Installer runs whenever the version of Word that you start is not the one that is registered.

Dakle izgleda da je to regularno ponašanje (ili možda može nešto da se sredi kroz registry?). Uglavnom, mrzelo me je da se dalje petljam pa sam prešao na Office 2007, uveravajući sam sebe da je to brži način da se naučim da plivam. Interesantno da nije bilo ovog problema sa beta verzijom.