System Prefs > Security > Firewall
Click the little "+" icon near the bottom
Choose your app
Tell it what to allow/disallow
Done.
that only gives the option to allow or disallow incoming connections....
im trying to set up azureus, and need to make sure my specific ports are open.
I like to leave the firewall in stealth mode.
it all works until i enable stealth mode, (actually setting up ports in Transmission) then Transmission says that the port is stealth.
without stealth enabled, the port is reported as open in Transmission.
I prefer the firewall in Tiger, it was much more configurable, Leopard seems to have over simplified it to the point of not really being useful!