Just don't download anything that someone is sending you in a email even if you know the person get it through a im program so you know it's them and don't download anything from strange areas and your fine.
Hell I don't have a viri scanner installed and if I think I got one then I do an online check, but viri scanners are a pain when it comes to gamming. Also a router is useally good enough fire wall protection as the odds of getting hacked by an amazing hacker that you don't know is rare.
And just for the records I havn't had one viri for 2 years now so I think these steps work mint