Get BCWipe and TrueCrypt. Keep any and all personal data in an encrypted partition, then hide the partition in an encrypted volume. Its like locking the door and then concealing that the door even exists. Have BCWipe run every night to wipe Swap file and etc. De-frag often. Encryption and wiping 'unused' or 'garbage' portions of your free space and managing your file system well also makes the ecology of your system hostile to malware, which depends on using free space 'out of sight' for its nefarious purposes. Expose NOTHING to network shares.

Norton AV is a good product in what it does, but its performance footpint and effect on system stability has been historically a problem. McAfee is not as good in security, but I have seen less performance and stability problems with what it does. SpyBot 'search and destroy' is a must.

Firewall, OS updates and good user policy are the best defenses against malware, everything else is just fortifying the existing works. Nothing wrong with fortification, but the fortifications are only as good as the foundation. Read up on routers and home networks before you install one, especially wireless. The devil is always in the details.

No plugged-in system is entirely secure, but by taking the basic steps, you can secure against the worst threat: Script Kiddies and root-kit end users who are (usually) just idiots out to wreck havoc. A good hacker can always get you unless you are a security ninja or a 1337 hacker yourself. But those guys are less concerned with massive havoc, and more concerned with specific targets in my experience. IE- don't worry about the Saber-tooth tigers who don't prey on the little game, worry about the plethora of wolf packs who do.