If you are running Norton Antivirus then yes i would deffinately uninstall it in favour of AVG, as for a good firewall I can highly recommend ZoneAlarm,its free too.
I took off Norton AntiVirus and now my PC runs faster and switches off almost immediately. I installed AVG and Ad-Aware Free Edition for Spyware. As for a firewall if you run Windows XP you have one for free. It just needs setting up through Control Panel