The product does require you to understand the basic of IP networking (use the simpler NoobProof version if you don't have this basic knowledge) but does an effective job of configuring a network level firewall for OS X 10.5 Leopard.

Since 10.5 switched to the application-level firewall instead of network-level, the customization does not provide the necessary protections for those who may be running one form of a server or another (http, dns, mail, etc.)

Two thumbs up for this application, which once you get past the learning curve of the application and what it's doing, is the best I've tried so far.