You need to run an Ethernet cable from the new router's Internet port to a port on the old router and assign it a static IP address, e.g., 192.168.1.2. Then configure the new router to assign DHCP addresses on a different network like 192.168.2.0 and add a router on the old network so that it routes traffic to 192.168.2.0 through 192.168.1.2. If you want to use it as an access point, then read http://www.dslreports.com/faq/11233. No matter the configuration, you need an Ethernet wire between the routers.