Router connection

I have a Cisco router that has two Ethernet connections, but I supposed only one can be used at a time. One is a 10Base-T (RJ45) connection and the other is an AUI Ethernet port. It also has one WAN serial connection. I have a broadband cable modem that outputs to a standard Ethernet cable (RJ45 connectors). I want my router's Ethernet0 line (either one.. doesn't matter) to connect to a switch or hub of mine. But I also want to connect the router to the internet, through the serial WAN connection. How can I take my broadband cable modem and connect it to my router's WAN connection, to provide internet access to my network? The cable uses RJ45 cables and the serial line on the router is a V.35 cable end. Is there any medium to connect the two? How would I go about providing WAN access to my router? Thanks, if this makes any sense.