Many thanks Lame, problem solved.
I used the Symantec Removal Tool as given in Crashdive's post of 22.7.01. The Mcafee cleaner that I had used previously didn't restore the Rundll.exe file that is required to open most files. The Symantec tool had no problem giving me this back.
Everything seems OK now.
[ 20 August 2001: Message edited by: Wet Power ]