I use BBIagent since a couple of days, it's a free linux based Firewall / NAT / proxy / DNS / router it fits on a 1.44 MB floppy, doesn't need a HDD or monitor. Runs on a 80386 with 8MB RAM and is very fast.
The only prob / bug I have is that it disconnects sometime without reason. (Vorlin and I are searching to find the cause)

here's some nfo on it:

http://www.linux.org/apps/AppId_7658.html

BBIagent homesite:

http://www.bbiagent.net/