How to route 1st DD-WRT through 2nd DD-WRT on LAN

Hi,

I'm trying to connect one WRT54G DD-WRT to route through another WRT54G DD-WRT. The first has a closed WIFI and LAN 192.168.1.x and the gateway info and static iP of our internet provider. All office machines are on this first LAN and its protected WLAN (hidden SSID, WPA2). The 2nd router I'm trying to setup as a public hotspot, but I want it isolated from the 1st router LAN.

The easy (and not free) solution is for me to ask the provider for a 2nd office static IP and use that for the 2nd router. That would be complete isolation.

Obviously there's a way to let the 2nd router have a static IP on the 1st LAN, route its open WIFI through the 1st router LAN and not allow access to all other LAN IP addresses.

I can't figure out the DD-WRT settings needed on the 2nd router to make this work. I want it to have a static IP, like 192.168.1.99, but serve DHCP range 10.0.0.x on the open WIFI.

Can anyone tell me the settings in the 2nd router's DD-WRT Basic Setup page I should be using, as well as whether it needs to be configured as a Gateway, Router, or something else?

Thanks!