It seems I may have been a bit hasty checking out BHODemon.
I have now shut off all BHO's, deleted cache and cookies, closed and restarted the browser (IE6). I have been working for about an hour now and no sign of the dreaded HelpFind.Info popup. So it appears that the BHO's were the culprit.
hiwatt - it's worth a try see manarth's earlier post
Thank you everyone for the help!