Antivirus: There are many Antivirus products available to chose from. I have used many of these antivirus programs and have found AVG the best free antivirus software out there. The new release includes Anti-spyware, e-mail scanner and link scanner. http://free.avg.com/us-en/free-downloads

Firewall: The most popular free Firewall used is Zone Alarm. Remember this is an optional firewall other than using Microsoft's Firewall and will take some user interaction to get set up.

McAfee WebAdvisor Advisor: Don't select any Search Engine links without McAfee WebAdvisor installed. Here is where to get it. http://home.mcafee.com/root/landingpage.aspx?lpname=get-it-now&affid=0&cid=170789

OpenDNS: Add this additonal layer of security to your Web browsing by setting up DNS on your computer or router through OpenDNS. Make sure you select the link "Learn about Home Network solutions". https://www.opendns.com/home-internet-security/

KeyScrambler: Anti-Keylogging protection. Protects all of your inputs in your Internet Browser of choice. Check out link below for details.
http://www.qfxsoftware.com/products.htm

Note: As you can see you don't have to spend money to protect your computer but it's okay if you buy additional protection from these software companies if you think its necessary.