Do I need to remove Norton AntiVirus 2011 before installing 2012?
Norton Antivirus 2012 is designed to install seamlessly over NAV 2011 and to preserve your settings. It is the recommended way to upgrade unless you are having problems with your current installed version. You do not need to remove the older version first if everything is working properly for you.
For minimal conflict yes. I always prefer to uninstall the product completely (using add/remove AND the Norton Removal Tool)before upgrading.