http://www.ipcop.org/
http://www.smoothwall.org/
The two are very similar and have the same roots. SmoothWall offers a
commercial version with official paid support. IPCop does not.
Commercial paid support for IPCop comes strictly from 3rd parties. In
your case I'm guessing you don't want paid support, so either should be
just fine for you. Both will be better as dedicated firewalls than
building a f/w from scratch with Debian.
--
Stan
Both are extremly good firewalls. I built a firewall system from scratch using Gentoo. The learning experiance is good building a firewall system, and dont discount Debian from the job. A non X install, and some command line knowledge, and you will enjoy the fact you created it, and not locked in.