I have been working on several family members computers lately. Many of them having either expired AntiVirus and/or no AntiSpyware. As a general rule here is the software that I install to protect personal computers. General rules for Windows XP.

Grisoft AVG 8.0 Free Edition
http://free.grisoft.com

Microsoft Windows Defender
http://www.microsoft.com/defender

McAfee SiteAdvisor
http://www.siteadvisor.com

Mozilla Firefox
http://www.mozilla.com/firefox

Your family would have to be looking at porn everyday to get infected after these changes. I haven’t had a problem. The AVG is set to run its full scan at 11PM so it doesn’t interfere with anything.