Not to start anything here but... http://web.archive.org/web/200412121.../grcsucks.com/

Is the Wan of the RT31P2 using dhcp to get its address by chance?

Your WRT has nothing in the "gateway" portion of its DHCP server according to your post. This should be its lan address. 172.20.0.1

Id also turn off dns forwarder if its on. I believe some routers have problems passing dns queries between the "client" and the internet when the forwarder is on... worth testing anyway.