Download AVG Free and install that.
Along with AVG and Zone Alarm firewall, we recommend you have installed an anti-spyware program that offers real-time protection.
Windows Defender gives you that but Spybot S&D does it better. My advice is to remove Defender, and have Spybots SDHelper and TeaTimer services running. In case you dont have it, this is the latest version. (1.5.2)
MBAM will offer good extra protection as a scanner, but the free version does not give you real-time protection.
WinPatrol will guard your start page from Hijacking and alert you to new start up programs. It also includes a Startup program utility, where unneded programs can be disabled from starting up automatically.