Beware of Norton. Symantec does NOT provide engine updates as part of their subscription plan, thus forcing you to buy a new Version every year or so to be fully protected. An out of date engine, even with new signatures,
will not detect some new threats. Case in point: NAV 2003 does not have unpackers (note: I'm not referring to zip/rar/tar/etc, those are archivers) and cannot detect virii in packed executables, even if it has the defs for them. NAV 2004 has some unpackers, but not as many or as good as 2005. On the other hand, McAfee provides engine updates to anyone with a valid subscription. Theoretically you could still be running Version 4.x and still be fully protected. I think most other vendors also provide engine updates.
Also note, free AVs are worth the money you pay for them. They're ALL pathetic compared to the likes of Norton, McAfee, and Kaspersky. Then again, NOTHING compares to Kaspersky. It has the best detection, hands down. It also updates the most often.
The next and most important thing you'll want is a router. Home routers are cheap, quick, and easy to configure. There is no reason not to have one and I'd rate it the most important layer in your security setup. ANY* soho router, whether it says it includes a firewall or not, will block unsolicited traffic. In other words, it'll protect your network from the worms that rove the internet these days.
Routers only do half the job. They block unsolicited incoming access, but (SOHO routers at least) can't prevent an application on your system from reaching out to the internet. For that you'll need a personal firewall. I recommend Kerio 2.1.5. Learn it, it's worth it. Otherwise, go with ZoneAlarm. No, you don't need the Pro Version, it's kitchensinkware that includes a lot of crap that doesn't belong in a firewall product, IMHO.
If you're running Windows 2000 or XP, it might also be a good idea to consider an anti-trojan application. Anti-virus scanners are all well and good, but many of them simply can't deal with trojans. I would recommend you visit
the DSLReports Security forum and check out the FAQ, you'll find links to anti-trojan vendors there.
Finally, realize security is very much a risk-assessment exercise. If you're an average user and use IE 6 on XP, you'll want all the protection you can get, and should have a router, firewall, anti-virus, anti-trojan, and Ad-Aware, Spybot S&D, Javacoolsoftware.com's SpywareGuard and SpywarebLaster, and IE-SpyAd. If you don't use IE, you can afford to ditch the anti-spyware apps.
In a nutshell, you
need a router (scale 1-10: 10), it would be a
very good idea to have a firewall (1-10: 9), and you definitely
want good AV protection (varies depending on your habits, really. Generally: 7). AT protection might also be
a good idea particularly if you run 2000/XP, as ATs are particularly powerful there. (1-10: 6)
*I say any because you'll be hard-pressed to find one that doesn't at least to NAT, and that in itself provides a lot of protection.
Interesting trivia: KAV has the best detection and most frequent updates in large part because of a very active userbase. KAV Users regularly submit samples to Kaspersky labs which, if undetected, signatures are quickly developed for. Generally speaking McAfee and NAV Users aren't so vigilant, and I'd venture to say 90+% don't even know about how to submit suspected malware to their vendor. You can learn more about submitting malware at the security forum above.