Well, it is back. Final try yesterday, lots of 'ignore that file' and at around 2200 I was left with a mini XP splash screen, eggtimer and occasional disk activity. No progress for 1 hour+. So on with the jimmies and bed hat and socks and I left it running overnight. In the morning, computer still on but Windows had shut down. Tentative push of power button and an agonising crawl into my old Windows over 20 minutes. No Windows update available -'Error 1083'- (tried 'registering' lots of files with no improvement), and emails looking trashed. I ran the SP3 update again off the separate SP3 update disk, and I got Windows update. I am in the process of recovering the OE messages (folders.dbx stuffed). So far all else seems ok
I just wish I knew what had caused it!