I've been using Norton AV and Firewall since 2003.
I currently us the MS Spyware app but it has not found anything yet.
I've not gotten a virus ever.
I've never gotten a Spyware infection that took more the 5 minutes to remove, ever.
All this while surfing p0rn with no reagards.
XP SP2, Some kind of AV/Firewall, and the MS spayware app shold keep you safe and secure.