Whoopee!

Thanks, Mick, ComboFix sorted it! It took a while to get everything ready (including finding a download of the XP boot file to allow installation of the Recovery Console as this machine came with recovery CDs instead of XP), and a while for it to run... it will take even longer wading through the logfile to see what the problem actually was, but everything seems back to normal on this machine.

It found a couple of 'robust processes' running, and I'll let you know what they were when I find out.

No, there wasn't anything abnormal in the hosts file...

Now to try and sort the other two... back later!

For the record, Mudcat got there before the Tech Forums and Webroot's helpdesk... I'm eternally indebted to you lot!