The only thing norton does well is antivirus...
Having firewalls such as zone alarm on your PCs is definitely good. Partition the network and contain the damage if one machine gets "compromised".
Just today, Outlook let in a whole pile of nasty on my little sister's computer.
Most of the machines were perfectly fine since they've got local firewalls and/or run linux.
It did get our net service cut off for a few hours today, but its all settled now.
A little "format c:" and switching 'em away from outlook to a nice Online mail service, and all is well
