On Mac 10.4, we could use the /usr/libexec/FirewallTool to enable the firewall rulers. But there is no /usr/libexec/FirewallTool on 10.5 again. What daemon or service is used to replace the 'FirewallTool' on Mac 10.5?
You can edit the ipfw rules still but the 10.5 firewall is based on firewalling applications not ports. I'm not sure how it ties into ipfw but it's still there and able to be used for port based blocking.