Hi,
Just to add to this thread I'm experiencing the same issue while testing patch Security Update for Office 2003 (KB951535). Here's some more information on what I'm receiving. (I'm not trying to hijack the thread just offering some more info!

)
In event viewer I have event 1023 with the following message -
Code:
Product: Microsoft Office Professional Edition 2003 - Update '{CA93C194-87EF-4A2C-B2DE-99F3AF4CD36A}' could not be installed. Error code 1642. Additional information is available in the log file C:\DOCUME~1\green_d\LOCALS~1\Temp\OHotfix\OHotfix(00002)_Msi.log.
I tried to run the patch on my machine manually and recived the following message
Code:
The expected version of the product was not found on your system
Somebody slap me just worked out why this is working the error message was telling me! We only have SP2 in our office installation and the patch requires SP3
I've continued to post this just incase there's someone out there as blonde as I am!

might save them any embarrasment asking!
Cheers!