HELP PLEASE!!: Ipaddress CHANGE using Netgear Router, Vonage V-Portal Router, and Cable Modem?

Can anyone tell me how to do a ipaddress change?? I am using a Netgear router, a Vonage V-Portal router, and a cable modem. I was able to change my ipaddress at first when I was just using a Netgear router and my cable modem by just changing the MAC address in the Netgear router. But snice then I got Vonage which came with a V-Portal router. My cable modem first connects to the V-Portal router then I connect my Netgear router to the V-Portal. I tried the same method of changing my Ipaddress by changing the MAC address in my Netgear router but for some reason the ipaddress remains the same. CAN ANYONE PLEASE HELP ME ASAP!!!??HELP PLEASE!!: Ipaddress CHANGE using Netgear Router, Vonage V-Portal Router, and Cable Modem?
If you use a router, the only IP address that matters is the ip address of the router interface that faces the carrier(it is assigned by the carrier). The address of the PC will be assigned by the router, and will be of the form 192.268.x.x. Changing your macaddress should change the 192.168.x.x address on the PC - but the carrier still sees the address assigned to the router - not the address on your machine.HELP PLEASE!!: Ipaddress CHANGE using Netgear Router, Vonage V-Portal Router, and Cable Modem?
You would need to change the MAC address in the V-Portal. But there is no reason you should need to do this. Why do you think you need to change your IP address?