A couple of things could be done to vastly reduce the number of systems being infected. First, Windows should come with all ports disabled allowing the user to only open specific ports for specific applications. Also, a _good_ firewall software akin to Tiny Personal Firewall, and not that garbage that MS put in to XP.
The last option is simply to buy a non-Windows PC. There aren't very many virii written for Linux and many distros come hardened.