This article describes how to set up a very simple desktop-firewall on Linux (Fedora).  Step 1: make sure iptables is installed on your system:# rpm -qa | grep iptables
iptables-1.4.1.1-1.fc8&nbs [ ... ]

Let's assume that you have a directory "test" containing the following files:  [root@blackmod test]# ls -la
total 8
drwxr-xr-x.  2 root root 4096 2010-03-10 06:11 .
dr-xr-x---. 11 root root 4096 20 [ ... ]