Plug in 1 ethernet cable to any port of both modem/routers, as long as it is not labeled "Internet" on that port. The ports do not need to match numbers at all.
The router that currently gets an internet connection: Make the i.p. address 10.0.0.2
The rounter/modem you want to turn into the access point: Make the i.p. 10.0.0.3
The router/modem with ip of 10.0.0.3 must be set as "Automatic DHCP"
Subnet mask of 10.0.0.3 must be 255.255.255.0
Username and Password must be on 10.0.0.2 router/modem.
10.0.0.3 modem does not need username and password.
Disable wireless of router with 10.0.0.2 as you will not need that, and will access the internet wirelessly through the 10.0.0.3 one.
If needed, put a WEP security on the 10.0.0.3 router, but not on the 10.0.0.2 .