It turns out that Linksys' WRT54G router runs linux under the hood, which may not seem cool at first glance, but that means that under the GNU license shananigans, Linksys has to make the source code available to any one that wants it. You can get it at http://www.linksys.com/support/gpl.asp
What it also means is that people have already been writing their own firmware for the things, and doing cool things with them--like enabling a ssh remote login shell... You can do anything with it!!
I've been having fun