Great,... however.... make a very very good interface AND a "tab" where you can edit the .conf files associated with the firewall... Even if you create a GREAT gui for the configuration of the firewall it will always be nice to view and edit the config manually... especially when working on security. When editing in the GUI you will be able to view what you are working on and how it changes your conf files... This will learn users also how they can do this from a command-line using VI.
There's a program called "firestarter" that will help with setting up your firewall. If I remember correctly, it is in the Ubuntu repositories for download. I used it a while back when it first came out, but I have since learned the command lines to create my own init scripts for ipchains. I hope this helps a little.