Unable to get online

Here is my problem.I have a RH 9 box that I also use as a router. My
home network is comprised of 3 machines,192.168.0.5 - 6 - 10, the
gateway for those is 192.168.0.1, the gateway for that one is my cox ip
address.

In the router I have 2 identical nics, Linksys is the brand.

I can ping all of my boxes and from the boxes I can ping eth0 with the
cox ip address, but I can not ping past that point. The nameservers I
can't also
ping from any machine.

What I did was I built up an old machine to replace my router so I can
use it to experiment with. I hooked up the old box and gave it the same
ip address as my router, that is when I lost all internet connectivity.

I reconfigured the network settings, I even reinstalled RH 9, but I
still can't get out.

Anyone can point me in the right direction? I red and re-read the
Linux Networking how-to, but that only includes up to the 2.2 kernel,
though I figured the basics are the same.

Any pointers are appreciated.

TIA

FrankM