Okay, I see two ways to go about this:
1.) You for some reason need two incoming IPs, and this is why you're hanging onto two routers. Either a.) call the cable company and get them to assign you a 2nd IP (usually $10/mo. or so) so both routers will work, or b.) try to figure out how to forward different ports to accomplish the incoming traffic you need.
2.) You just need more internal IPs than the one router is giving out. This could possibly be fixed by using the main router to hand out ALL IPs (set the range bigger so you have more, probably 192.168.0.2-192.168.0.254), and turning OFF DHCP on the 2nd router and just using the ports other than the uplink port as a switch upstairs.
3.) We may still not understand what you're trying to do with the IPs.
The two problems you have going on:
1.) The cable modem won't give real IPs to two devices.
2.) Two routers linked together nearly always have problems doing NAT (network address translation) twice. The translation of a translation doesn't go through.
A pun is a bad joke.
