The reason for the router is that a router will use DHCP and assign IP addresses. Your outside IP hits the router, the router uses NAT, which essentially hides your internal ip from the outside and routes traffic to the correct host on the network. Once you have the router plugged in properly, reboot the cable modem if it does not give you internet instantly and once it comes up your internet should work flawlessly. The reason Dabudkrew's works differently is due to sticky ips and PPOE. PPOE requires you to log your modem into the internet before it will work. You may have to emulate the mac address of the DSL router to be able to access it after the installation of your router.
There, I feel better.