By and large most of Symantec's software (Norton) is resource hungry and they all slow down your PC, more so with Norton.
The Norton firewall is recommeded and can hold its own with BlackIce and Zone Alkarm, however with Zone Alarm its important to contact your ISP or broadband provider to get the IP address for their system 'heartbeat' as Zone alarm will shut the system down if you don't set up your IP's hearbeat as an allowable inwards 'ping'.
Hearbeat is common with providers to enable then to check quality, response time, and monitoring time on line etc.