I use AVG ( free ) and Zone alarm ( free ) on one machine (win 98 ) and Norton Internet Security Suite on my XP machine as well as Spybot & Adaware. All avaialable if you search using Google.
Both machines have survived 8 months of broadband life.
I also have a hardware firewall on my router but that is a recent addition.
Matter of choice which way you go - I couldn't afford 2 x Norton so went for the freebie on 2nd machine.