Upps..Sorry ...I forgot to posted second alternative IPtables firewall..this one easier to set up too
[quote] One such tool is gShield which can be downloaded from http://muse.linuxmafia.org. gShield has support for both ipchains and iptables. If you're using ipchains you'll need to download one of the older packages as the current package for gShield uses iptables. Configuration is as easy and answering YES or NO in a text file. A graphical configurator for gShield also exists and is available at the website.[ /quote]

gShield is an iptables firewall for use with the 2.4.x series of the Linux kernel. It is easily configured through a single, well commented configuration file. If your needs are more minimal, see levy, a iptables ruleset generator.
check out their link http://muse.linuxmafia.org/gshield.html

cheerss