What Justin said. BOTH posts. Norton always seemed to be a way to pay money for instability.
I'll only add, that REALLY paranoid users of Windows also download Spybot Search & Destroy, Windows Anti-Spyware, and Spyware Blaster. And a firewall like Sygate.
Lavasoft's Ad-Aware, Spybot Search & Destroy, Windows Anti-Spyware, Spyware Blaster, Sygate firewall, Grisoft AVG and switching to Firefox/T-bird for browsing/email has kept my (PC) clueless dad from turning his WinXP box into a spyware/virus-infested brick. Automate what you can (which is ~75% of updates/scans, with the free versions) and print out a regimen for the maual tasks. It has been 10 months of malware-free computing for him.
A similar regimen exists on my wife's laptop. She soldiered on for years using linux, but fianlly I got her the laptop I promised. She's been good, lo these 8 months. Still uses Firefox/T-bird.
Switching to Firefox/T-bird helps keep the malware from getting on your machine in hte first place. IE/Outlook is the computing equivalent to walking into a pack of wolves wearing trousers made of bacon.