Avast or Avira would be good. I've used both. Microsoft Security Essentials (Beta) is what I'm
using now. You could maybe try that. Here is the link:

http://www.softpedia.com/get/A.....ials.shtml

It's the free replacement of Live One Care. The final release is due by the end of this year.

Clamwin is a free and open source antivirus program, if you're into that sort of thing.

http://www.clamwin.com/

Clamwin doesn't have a real-time scanner (very important for a non-geek).
ESET NOD32 only has a free 30-day trial.

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I will check out AVG and Avira. The less complex, the better in this case. (Of course the quality is very important.)
The Microsoft Security Essentials, I will have to look into. I don't know how I feel about it still being in beta. This individual is not very tech-savy.

@taybay
I used to play the game your avatar represents A LOT when I was younger.

Well,the best or amongst the best consistently is Avira, as indicated by tests from all sources,for actually blocking virus,a bit better than Avast.
I've run it for some time -excellent-light- doesn't use many resources.

Also running Threatfire free from PC tools-excellent.
ThreatFire protects by intelligently blocking behavior consistent with that of malware such as viruses, worms, trojans, spyware, adware, rootkits, keyloggers, and buffer overflows.
It isnt designed to replace the antivirus,as works differently and its blacklist isnt as big or active .
Its a HIPS type behavior blocker rather than a list blocker.
The idea is to run it as well as an antivirus-no problems as both are light.
Where one doesnt detect,the other should.

If set at default,neither require much user interaction and are very simple