Cox supplies only one external IP address per residential account unless you are on Ultimate.
Without knowing the specific camera system, I can only give general answers. IP cameras will pickup internal addresses using dhcp from your router/gateway. A common way to access them from outside your home network is by using port forwarding. You may want to assign static addresses to your cameras to facilitate port forwarding. This all should be explained in the camera's installation manual.
The internet connection would only have one IP address through the modem, with a router however it can issue connections to up to 254 devices at one time. If you are trying to connect remotely through a router the information AllenP gave is correct.