System: Windows XP Pro

Browser = Google Chrome ...because I never liked IE (too slow and too much screen space eaten up by the browser itself) and Firefox has become slow (started using it when it first came out and abandoned it over a year ago).

Firewall = Windows XP Pro firewall ...because it is simple (but not necessarily optimal)

Anti-virus = Avast (free, effective) ...I Used to have AVG (also free) but abandoned it because I felt it was slowing the system down too much.