Thought I would chime in.

Yes, a hardware router/switch combination, which your links point to, is generally cheap these days. However I wonder if you could get more functionality by using one of the PC's as the router and then a separate, and perhaps less expensive switch or hub.

This would involve placing a PC running say, Coyote Linux between your cable modem and the switch or hub, then connecting your other PC's to the hub/switch. Great use for an old PC.

I have an old P155 running CoyoteLinux and an old 5 port hub to which my other 4 home Linux/Windoze boxes (and a PS/2) are connected. Not pretty but it works great. I basically put two network cards in the old P155, the Coyote runs off a 1.4 floppy and set and forget.

You could just as easily place any linux box running Knoppix or whatever in the line, set up iptables, or one of the firewalls and still use the router computer for other purposes.

The only reason I didn't buy a router/switch was because I had the other hardware on hand.

If you search the forums here, you can find plenty of posts with links to Coyotelinux and such. rickenbacherus knows this stuff well.

A few links that might be helpful :

http://www.coyotelinux.com/
http://www.squid-cache.org/
http://lrp.steinkuehler.net/