Its strange that some folk have problems with Norton and others seem to get along with them fine. I'm probably inviting all sorts of trouble, but I've never had a single issue. Last week I installed the AV 2005 upgrade to 31 machines which were running 2004 professional. All went without a hitch.
I have also recently uninstalled 2004 versions of the Firewall and installed 2005. Again no problems.