Leopard firewall issues:

Symptoms:

• The firewall will ask you if you want to allow configd and mDNSResponder when you boot up.
  
• Adding the above to the allow list for applications does NOT fix the issue.
• Restoring the com.apple.kerberos.kdc keychains does NOT fi the issue.
  
• Setting the firewall to "allow all incoming connections" temporarily fixes the problem.

Probable cause:

• You removed the battery from your machine, or let it drain, or the OS was not shut down before powering off the machine.

Solution (for me):

• Reset the firewall configuration by restoring /Library/Preferences/com.apple.alf.plist

Edit: Nope, that didn't fix it either. And coreaudiod is on the fritz too. I'm thinking of just disabling the alf altogether (e.g. prevent it from starting in the first place).