One powerful and free anti virus measure you can take is to not run a Microsoft email client. I suggest one of the Mozilla variants. One of the ways many (most?) viruses propogate is by performing lookups in the Microsoft email client address book and sending themselves to those addresses. I am not aware of any virus that directly attacks or takes advantage of the Mozilla email client.
Interestingly many young people will give you a blank look when you mention an email client as for them the web IS their email client.