|You have two scenerios that would work.|
If connecting your router to the combo modem you put these ips in
lan 192.168.0.1 <-note the different subnet. You can't have the same subnet on wan and lan as given in previous example.
enable this routers dhcp server to serve out the following for the lan
2nd scenerio would be to connect the router combo lan port to a lan port on your router [as referanced by RTAdams89] This turns your router into a glorified switch [and wireless AP if its a wireless router]
config is as follows
no wan ips
disable dhcp server
assign it a static ip of 192.168.1.253 so you can manage it via the lan.
Ip will flow from the combo unit [if its dhcp server is enabled] to all your lan clients.
Depending on isp and if the serialize the connection to your pcs mac address you may need to clone your pcs mac address to the routers wan interface concerning scenerio 1
Do understand with the router/combo lan ips not being public you will not be able to host a web page or do port forwarding. You can only do those if the address you get is public.