Have you considered using FREE anti-virus and firewall software such as AVG or Avast (anti-virus) and Zone Alarm (firewall)...
AVG FREE - click here
Avast FREE - click here
Zone Alarm FREE - click here
Personally I use the free versions of AVG and Zone Alarm along side spybot to keep my system protected. Again Spybot is also available to use for free, but is more "donation ware" rather than free.
I've also recently tried Ccleaner to remove obsolete files and registry entries after reading good reports about it on here.
Hope this helps. ;-)