Office 2007 SP1: Obscure workaround for completing installation

I tried installing Office 2007 SP1 this morning, but no matter what I did, I got some variation of this error, conveniently 98% through the installation:

Product: Microsoft Office Enterprise 2007 -- Error 1935.An error occurred during the installation of assembly component {04E73476-518E-4B6A-8E10-021A00078847}. HRESULT: 0x80131047. assembly interface: IAssemblyCacheItem, function: Commit, assembly name: Microsoft.Office.Interop.RandomOfficeComponentHere,
fileVersion="12.0.6211.1000",version="12.0.0.0000000"...

The first time I got the error I googled and came across posts that said to repair Office 2007 first.  So I did that.   Then rebooted.  Tried again.  Another error.  Looking closer at the event log entry I saw that it pointed the finger at InfoPath, so I uninstalled InfoPath, rebooted, and tried again.  Same error, but now it pointed at PowerPoint.  I could see where this was heading - soon I'd have nothing left to upgrade...

Finally I found this series of posts; I am not sure which part of these two steps worked, but the following combination finally did:

• I first started the Office Source Engine service (which was set to Manual).
• I then inserted a CD in my DVD drive AND
• mounted an ISO (the original Office 2007 ISO) in my Virtual CloneDrive virtual drive (this part may or may not be required, but I believe it is).

Installation complete.

(YMMW.)