SULIS  You really shouldn't be forwarding on files of which you know so little but if there's an unprotected Windows machine out there you can be fairly sure that it will already have been infected by a Windows collleague. It's not your job to cripple your own Mac in order to protect Windows users too stupid to have installed their own anti-virus software.  
(Version 1.3.2)

SULIS  iAntiVirus is nothing like a condom. It won't catch any Mac viruses, either the ones that don't exist or the ones that haven't yet been created.  
(Version 1.2)

SULIS  "If there should be an aggressive new virus out there, I reckon that the chance of either aforementioned software on a Mac catching it may be no better than 50/50."

Actually it's zero. Anti-virus software can only detect a virus of which it's already aware. Any unknown virus is undetectable until the software is updated to recognise it. Since there are currently no known OS X viruses there is - as yet - no good reason to install Mac anti-virus software.  
(Version 1.2)