Firewall: Download ZoneAlarm from www.download.com
. It has a very simple interface, and it is top-notch protection (many internet protection suites use a version of ZoneAlarm).
Spyware: Download Spybot and AdAware from www.download.com
. Be sure to 'immunize' with Spybot. Update them weeekly, and scan with both weekly. Also, switch to Firefox if you haven't already, as I seem to get next to no adware/spyware since I did.
Anti-virus: Download a free trial of eTrust AntiVirus from http://www3.ca.com/Solutions/Collateral.asp?CID=39914
. The site says a month free trial, but I have been told that they are giving a year trial again.