Thank you for that Saab Dastardand Quartz-1. I'm sorry CATIII-NDB but I'm not certain your posting related directly to my problem - probably because I didn't make myself clear - but thank you anyway.
I'll go to Makro and get myself a relatively low capacity external HD in the hope (and I'll try to confirm it too) that it will work with USB 1 and that it's below 128 Gb to, hopefully, avoid control problems with 98. Then I'll try to manage both a snapshot image and a data file-by-file copy onto a separate partition - phew! for someone of my limitations.... And I'll try to arrange a repeat every month or so.
I've seen a few back-up programmes for 98 spring to mind - Cobian Backup, Karen's something-or other, for example. I'll try to find an easy one!