In another section called An XP Reinstall And A Windows Update - Recent Lessons Learned, I mentioned a "device installer error" message that kept coming up when I clicked on the Properties for IDE ATA / ATAPI controllers in Device Manager.  That problem, as it turned out, had a weird cause and therefore a weird fix.

It started when I followed certain steps posted at an url called How can I delete undeletable folders?, wherein a poster named "Dirk-Diggler" gave instructions for removing Netmeeting, MSN Gaming Zone, Xerox, Movie Maker, and Microsoft Frontpage from the Program Files folder.  Unfortunately, renaming SFCFILES.DLL to SFCFILES.OLD and then removing these folders in Safe Mode caused the "device installer error" to appear on reboot into Normal mode. Renaming SFCFILES.OLD back to SFCFILES.DLL and rebooting XP made the folders come back and the error go away.

I won't question it too much.  I'm just glad the main mystery is solved.