MietmaN while that may be true for you i haven't had problem with spyware or virus's without any anti-virus or firewall's
But im assuming we are talking about people who aren't exactly all too curious about their computer's(i suppose you could consider them computer illiterate). Some anti virus set to automatically scan frequently(not too often mind you) and auto update itself might be a good idea.
If you can find anything that runs in the background and does these tasks automatically without any user interaction(and shut itself up if there are any errors) you might find yourself being bothered less.
Worth a try i suppose and this has actually given me an idea for another program to make
EDIT: Also if any of these people aren't too heavy on ActiveX only supported currently in IE then perhaps installing Firefox and crippling internet explorer might also be a good idea.