That's it don't tell him about good Windoze anti-virus as as that'd be offering Winblows support and it'd be against the roolz.
Actually, if I did know I'd probably tell him. As far as I'm concerned there is no 'good' anti-virus, firewall, spyware removal tool, etc, anymore than there is a 'good' prison, or 'good' car accident. They're things you shouldn't have to worry about; you should just be able to use your machine, free of protective tools consuming 25% of your resources; Linux and OS X offer that.
I don't know of any 'we don't support Windows rule.' If someone wants to answer a Windows question be my guest, but I'm not going to waste my time when something else will just get corrupted, broken, or infected the next week.