After installing Service Pack 2, I started getting balloons on the system tray telling me that the status of Norton Antivirus and Firewall are unknown. I figured it was just the fact that it didn't work with Norton, but my Grandma's computer has the exact same version of Norton we do, and has no problems.

I am using Norton Internet Security Professional 2003. I am running Microsoft Windows XP Home Edition Service Pack 2.

I've noticed the same thing, sometimes it detects it, sometimes it doesn't. If you know you have antivirus installed and working just disable the nag screen.