It's gotten to the point where once your system is compromised, you might as well nuke it from orbit, it's the only way to be sure.
There's a lot of malware that'll rootkit your system, and it'll become almost impossible to properly sterilize the machine. Webs of programs that will monitor each others processes and restart any that are killed, same with watching registry locations, etc.
Having an AV solution is fine, but you can get a lot of the same benefits by using a bit of judgement. For example, put your machine behind a router. There's nothing about a router that makes you invicible, but it prunes about 95% of the casual attacks. Next, stop downloading and running every Golly-geened elf bowling executable your friends tell you about. If it ain't flash or HTML, I probably am not going to run it unless I've done the 30 seconds of homework on Google to find out if there's spyware included.
Oh, and don't use Internet Explorer. IE users bring a warm feeling to the sub-cockles region of a cracker's heart because the number of inherent flaws in IE's security model is so high.
Also, I don't care how paranoid you are about "teh evul bill gatES!!!", set your Windows machines to automatically download and apply updates. When Microsoft reprograms your computer to rips itself out of the wall socket and go on a killing rampage through your neighborhood, you can yell at me, but in the meantime, keep it patched to avoid unnecessary trouble.
Finally, stop using Microsoft Outlook. I know, I know, you like it that you can have a calender entry linked to a spreadsheet that shows exactly when you have lunch scheduled each day with collaborative online lunch planning (The rest of us just use this thing called a 'phone'), but it's a hive of scum and villainy. You'd best be cautious.
