I am looking at a side project (fun/educational) to buy a couple used
multiport NICs, select a Linux distribution, and make a router/firewall out
of some old hardware.  Has anyone out there tried this task and had any
success?  Suggestions on Linux distributions for just a router/firewall
configuration?  CD bootable versions?

Quick google search produced:

Linux router project (now DEAD)
BBI agent
Diet-Router
fli4l
floppyfw
FreeciSCO
Rock Router Linux
Sisela

Would be nice if anyone had some thoughts on these or other distributions.
My goal is to have a secure, solid, remotely administrable system.

Many thanks in advance ... as always.

Randy