First of all i need you to connect the PC your using to browse the internet to the router (at this point do not connect the net) when you have connected the Router to the computer load up Internet Explorer and type http://192.168.1.1
when connected to the router enter the username and password (if there is one) when the page is loaded look for Mac Clone it should be under Network.. It should look like:
Click MAC Clone once in this page click Clone MAC Address button.. at this point the router will ask you to reboot at this point plug your Internet Cable from the Modem into the Router and then proceed with the Reboot.. Once this has rebooted check the Internet in another Internet Browser i.e. Google for instance to check that it has worked.. If the following procedure has worked would you like me to connect Remotely to the router to make sure everything is set up for you as it should and set up Wireless so your neighbours do not connect to your router..
Hope that helps..