I think that some of you are continuing to miss the issue with viruses. You that think you understand the basic principles of trust and computing...never trust anything unless you are buying a machine and never loading any software...period. Malware (the term used to describe spyware, viruses, etc.) use an incredible array of devices to make it onto your machine, propogate itself, and attack your machine. You want as comprehensive a solution as money can buy. I'm all about freeware, shareware, etc. but the problem is, you need an entity that is vigilantly geared for keeping up with malware as it continues to morph. Unfortunately, volunteer efforts will never keep up with the pace the legion of professionals who are paid to spend all day everyday sorting out issues and programming against them. You need to buy a best-of-breed, comprehensive product, as rated by competent industry recognized security labs. Fortunately, these products are not expensive.
Occasional scans are not okay (a passive scanning method). You want active protection to keep malignant software from even getting onto your machine. Much like cancer, there is a threshold at which point, removing some malware becomes next to impossible--you can't afford to allow that to happen, unless you enjoy rebuilding your machine. Virtual machines are a wonderful device to contain potential threats. Use them as sandboxes to scan newly acquired software before moving them out of the sandbox. As I have said, you need to buy a best of breed security suite, however, much like contriceptives, your chances of success go up if you stack them--run as many scanners as you can (there are lots of free ones) against a new application before allowing it out of the sandbox.
Don't think you'll know when you have contracted malware. There is a class of malware called rootkits who's main job is to hide themselves from the O/S and security software. The second order of business is to propogate and infect, and the last order of business is to perpetrate deviant behavior. A favorite mechanism of Rootkits to survive is to replace something core to the O/S that is implicitly trusted, such as svchost.exe in Windows. When your machine is running, many copies of svchost.exe run on behalf of different processes. Some rootkits become "angry" when attacked--if you make lame attempts at removing them, they can lash out and do things like destroy the master boot record, preventing you from booting your machine. Malware sometimes employ teams of processes which look out for their brethren in order to keep the team alive--while you are attacking one component, the others are attacking your effort, attacking your system, and replacing the component that you just removed.
Look, unless you are an experienced expert of your O/S and quite skilled, you are likely not to even know that the malware is there until it avails itself to you in a way that you don't like. You are likely to unknowingly back them up in your archives too. Do not under-estimate the brilliance of malware writers. On the planet, there are several Einsteins out there who are unfortunately geared for doing damage. It is humbling when you fancy yourself to be an expert and then get infected by a rootkit that you are ill equiped to remove. I once identified a rootkit on my system and spent 6 hours collaborating with renowned Comodo experts only to find that none of us could remove it--I painfully rebuilt the computer.
Incidentally, I run fairly recent hardware and use ZoneAlarm's Extreme Security Suite on Windows 7. I have noticed no degredation in performance or stability, and knock-on-wood, I haven't had any issues for quite a while.
However, if you wish to increase the likelihood that you will continue to compute trouble-free, be a student of your O/S, be a student of the best-of-breed security suites and buy one that you are comfortable with. Be paranoid. Use a virtual sandbox as a scanning lock. Today, buy a best-of-breed security suite that actively scans all entry points onto your machine, and always, always, always keep your definitions up to date!
Oh yeah, to lyx...regarding the detection of 8 year old malware...those who forget the past are doomed to repeat it...good luck.
Be thankful for your challenges...if your job was any easier, someone else would have it.