Hi Microbell,
I did try to shut down Mc Afee, nothing changed, same pbms - but, following your idea, I uninstalled it, replaced it with ZoneAlarm so as not to be online unprotected... and everything's back to normal now!!
My browsers - both Moziall and IE6 work fine, no more crashing, all the websites accessible again, etc.
Problem solved (well I still don't know why McAfee did this as it used to work just fine with Win 2000 - but at least, I've got a computer in working order).
So thanks again!
K