Just got a friends PC to have a look at because it's going wrong and after discovering over 6000 junk files, 100+ viruses 15 diallers, 9 keyloggers and 380 malware programs I finally got it something like it was. It had no Antivirus, no firewall and no spyware protection as he said he couldn't afford it. I'm sure there are a few of us who haven't got the reddies to splash out on security software all the time, so I thought I'd compile a short list of decent free security products that should keep your PC in good serviceable condition.
The list is in order of effectiveness top to bottom.
Avira : http://www.free-av.com/
Jetico : http://www.jetico.com/jpfirewall.htm
NetVeda : http://www.netveda.com/downloads/index.htm
Malware Bytes: http://www.malwarebytes.org/mbam.php
Adaware 2008: http://www.lavasoft.com/products/ad_aware_free.php
K9 Web Protect: http://www1.k9webprotection.com/
Hope some of these applications keep your PC clean and free from errors