For help with firewalling under Linux, I suggest looking at
plonk.sourceforge.net

This is a very good script for quickly and easily setting up an ipchains
based firewall. (kernel 2.2.*) I haven't looked at the iptables
(2.4.*) version yet.

Another firewall script you might find useful is here:
http://heimdall.asgardsrealm.net/linux/firewall/
This one is for 2.4 only.

Andrew S. Zbikowski | http://www.ringworld.org
"We can learn much more from wise words, little
from wisecracks and less from wise guys."
--William Arthur Ward