It doesn't matter if you don't have a network. Even if it's just you, a PC, and a bag of chips, one of the simplest and most effective steps you can take to secure your home computer from all the ne'er-do-wells on the Internet is to put a router in between your cable or DSL modem and your system. The router makes your computer virtually invisible to the outside world. And you can get pretty decent ones CHEAP!!! Case-in-point: Newegg has the D-Link DI-524 AirPlus G Router for only $15.99 after rebate, shipped free. It should no-brainer. It's cheaper than most security software and doesn't require that you install anything on your computer that might make it slower or less stable. Read PC Mag's review of the router.

$15.99 too rich for your blood? How about $9.99? That's the price of a wireless router at CompUSA, and it has specs very similar to the D-Link's. PC Mag hasn't tested it yet, but the user reviews on CompUSA's site are generally positive. (Of course with the $5.00 shipping, the two routers end up only one dollar apart.)

Both of these are wireless routers, if you don't need the wireless part, make sure you disable it in the router's setup. And don't get sloppy and think getting the router means you won't need your anti-virus program or a software firewall anymore. They remain essential.