This might be a no-brainer to most, plus not being that savvy with the Terminal, I probably take a more laborious route here and there. I've been using Brickhouse
as my firewall for OS X since it also added easy support for internet connection sharing.
After upgrading to 10.2, in browsing around I gave Apple's firewall settings a look, but in order to do so had to first disable Brickhouse and restart. If another firewall is running, the settings for Apple's firewall are disabled and it displays an error message in the Firewall preference.
In playing around with the built-in firewall (opening up web serving and SSH), I realized it wasn't sufficient for what I wanted to do and re-enabled Brickhouse and started up again. I looked back at the built-in firewall preferences, saw that they were greyed out, error message about other firewall software running (just like before I explored Apple's firewall), and I was good to go. Unfortunately, after that, the other machine on my home network (a PBG3 connected via an Airport) was only able to utilize SSH and view web pages (only port 80, not any secure pages).
Well, even though the error message on Apple's Firewall led me to believe, at a quick glance anyway, that it was not active because other firewall software was running on my computer, it turned out that I needed to disable Brickhouse and reboot so I could click the "Stop" button on Apple's firewall. Once I did that, everything was fine again. So, even though Brickhouse was picking up most firewall settings, it seemed that the only traffic allowed on my LAN was what I had left open according to Apple's firewall settings, even though (I thought) it wasn't enabled.
What I thought was weird about this is that it seems like both firewalls were running. What is weirder is that even though with the built-in firewall's editor you cannot configure settings for a second ethernet interface, that was the interface being affected.
Although not an earth-shattering hint, if you've played around with Apple's firewall and another package, this may help you resolve any problems you've had since doing so...]