BTW, if you don't do at least weekly updates of your antivirus software, you're wasting your money to buy it in the first place.
Another thing to consider is whether you need a firewall or not. If you're connecting via broadband (cable or DSL), you should very, very seriously look at a firewall. While software firewalls help, you can buy 4-port hardware firewalls for under $200 that will also let you share your netlink with other machines (without them having to be DHCP slaves as is the case with WinXP/2K connection sharing.) For about $60-90 more, you can also have WiFi support (though personally I think wireless isn't really ready for more than the most casual use. YMMV.)
Antivirus protects you from bad emails and websites, but without a firewall you're totally exposed to hackers anyhow. Software firewalls like Black Ice Defender are an option, but they're not as safe as having dedicated firewall hardware. (There have been viruses which disable software firewalls and AV software.)
Contrary to what some might tell you, you should leave anti-virus enabled during WinXP updates or software installs unless it's very explicit about needing to have it disabled. When you run into such an update, install only that one update with AV disabled -- leave it enabled for the others. (Maybe 1/20 Microsoft patches require it to be disabled.) Even games should be installed with AV enabled -- there have been cases of game CDs being infected.
Or you can go whole-hog on Linux (the preferred solution.) *g*
