You should look into a program called Portsentry.
http://freshmeat.net/appindex/1998/06/26/898904215.htmlIts not exactly a firewall, but if you want to monitor and restrict access to your machine, it is an excellent security tool. Once properly installed and running, it will monitor selected ports (should only monitor ports not in use) and act as a tripwire. Once the tripwire is tripped, you can have it react in a number of different ways. The best defence it has is it drops the users IP into the /etc/hosts.deny file so the user cannot use any of the services of the machine, and also if you have ipchains installed it can drop the IP into ipfwadm's deny list. Then all the user's packets sent to your machine will be forwarded (without an ACK) to a fake IP on your internal LAN. So the packets will just time out. Your machine will then become a blackhole for his packets. He will no longer be able to even ping your machine. It will completely disappear to him. It's excellent for monitoring port scans and port specific scans (like netbus or backorifice).
I dont think E-Smith has the ipchains on it, or tools for compiling the portsentry program (it doesn't currently come in and .rpm file), but if your familiar with linux and can get these tools installed, it could be worth your wild.
B1tch-X