Norton for AV. Yes, it's good to have.

Adaware and Spybot for spyware. Yes, it's good to have.

Using and understanding the computer like a smart person with some common sense is even better to have. I haven't had active AV running all the time for the past year, never had a virus.

Also do a scan with latest adaware and spybot and have not found anything for close to a year now.

I have a linux firewall. Use Firefox for web and Thunderbird for email. A good understanding of how things work and what to be suspicious of. Good serving of common sense helps out too.