BOAC - Sub7 (the trojan described by Gibson) uses IRC protocol to let the hacker know what machines are online and available for use. It does not use IRC per se for any attack or hacking attempt. Zone Alarm will catch a lot of malicious traffic, but not all of it.
Most people feel comfortable with their anti-virus software, more informed people use a personal firewall but it's merely an annoyance that takes a few seconds to overcome.
On the positive side though, unless you sit permanently connected to the internet by cable modem or a T-line, you are unlikely to be affected.
In the meantime, have a look at
http://www.tlsecurity.net
http://www.megasecurity.org and in particular
http://www.megasecurity.org/Trojanlist.html
Whilst purporting to be 'security' sites, offering software for network pros to use to test their own system, they are quite obviously repositories for hacking software.
Download some of it... the capabilites are almost unbelievable.