You should uninstall Norton completely before installing anything else. You may need a special uninstaller from the Norton site if the usual uninstall has problems. If I remember correctly, avast! won't even install completely if it finds Norton present. Why ZAP if you just need a firewall? Are you also behind a NAT router? ZAF, Sygate PF, Kerio PF, Outpost, others have all the firewall functions you need for free. What ZAP vs ZAF gets you is mostly privacy stuff that is redundant with what you are already getting in Opera and Avant. I would install the firewall first, plug in the internet, then install the antivirus. Just don't download anything interesting until you are finished and you should be fine.