I am planning on setting up a Linux router what distro do you recommend?
it needs to be compatible with my old computer (future linux box)
-> 300MHz K-6
-> 128mb ram
-> 2 gig HDD
-> 4 mb graphics
Slackware would work. There's no GUI for iptables included though. I suggest devil linux or smoothwall, which are designed specifically for that purpose.
You're going to run into trouble if you don't know how to do either of those.
First I suggest reading up on TCP/IP, and general networking. Then read smoothwall's documentation. By then I'm sure you'll be able to efficiently setup a router/firewall, and learn something while you're at it .