Trying out IPCop as a firewall/proxy distribution on Junaid’s recommendation. It was only about 22MB to download and will run on virtually any type of hardware. Comes with a 2.4.20 kernel, Squid, a DHCP server and ssh login support. After the first reboot, brings up an easy to use web interface.
On the downside, it’s not easy to figure out how to customize it just the way you want and the performance doesn’t look that great (though that could be because of my hardware). Worth a look if you’re into these things.
FWIW, I set up a backup router at our company on a 300MHz box that was about to be thrown out with IPCOP. It’s been running for 3-4 months and has never given a problem. The VPN works like a charm too (too bad it doesn’t do PPTP or CIPE, though).