Help with a telewest modem plugged into wireless router

Hi guys I really need some help, we got telewest internet sorted out this morning however they fitted a cable modem with only 2 outs, one ethernet and one usb, since the router is downstairs we need more than one ethernet out and so i have plugged the ethernet from the cable router into the lan1 of the wireless router, this works fine for one person at a time, however if you plug in two people, one will see the internet connection on the router config page as disconnected. When it works the ipconfig/all box has an entirely different gateway than the non-working one, as well as a different dns server and mask. I was hoping someone could tell me if there are ay settings on a router to forward the internet through to more than one person. Thanks alot for your help guys. Ant.