Open source Firewal (GNU/GPL license), based on PC hardware

[ST Dragon]

Good Day,

I'm interested in setting up a 100% free open source software / Linux Firewal (GNU/GPL license), based on PC hardware, with a simple easy to use, install & setup interface, instead of buying an expensive dedicated hardware Firewall/router like Cisco.
At the moment I have a ADSL 2Mbit connection with a dynamic IP. My goal is to have content filtering to block all porn, sex, drugs, gambling, hate material, sites, etc...) and block all p2p software and ports (emule, utorrent, kazza, etc..) to all the business / corporate PCs (20 pcs) of my internal Lan network that have access to the internet through the ADSL modem / router.

The PC I want to use as a firewall is:

Intel Pentium III 800MHZ
128MB RAM
20GB IDE HD
1 x 100Mbit Lan Card
1 x 1Gbit Lan Card

I checked the following solutions:

Endian Firewall
http://en.wikipedia.org/wiki/Endian_Firewall

IPCop
http://en.wikipedia.org/wiki/IPCop

EBox
http://en.wikipedia.org/wiki/EBox

ClearOS
http://en.wikipedia.org/wiki/ClearOS

ClarkConnect
http://en.wikipedia.org/wiki/ClarkConnect

I also tried opendns http://www.opendns.com/ as an alternative DNS server in my ADSL modem / router settings and even though it has an excellent content filter and blocks everything, it can not however block any p2p software (emule, utorrent, kazza, etc..) and the ports used by them.

So, which of the above would be the best or are there any other even better and simpler 100% free solutions to cover all the above needs?

Any help will be highly appreciated.
Thanks in advance

[Ex-Cyber]

A DNS server can't block most P2P, since the software usually works by exchanging IP addresses among the peers (bypassing DNS entirely except perhaps for the server/tracker lookup).

I can't offer a specific recommendation, but a couple possibilities come to mind that you didn't mention:

Smoothwall: http://www.smoothwall.org/ (Linux-based)

m0n0wall: http://m0n0.ch/wall/ (FreeBSD-based)

[ST Dragon]

How good is this?

Untangle
http://en.wikipedia.org/wiki/Untangle