i reccomend you have a purpous in your experimentation with any *nix system. i chose a distro based off of redhat 7.1 for routing purpouses. the distro can be found at
www.clarkconnect.org its a fairly easy install and will run on a very minimal system. the only linux command i really needed to get started wa ifconfig, to get the IO and IRQ of the two network cards. theres very little official documentation but the forums are very helpful.