[Joxer]

It would appear that your router is behaving much like the old telewest wireless access points do - i.e. merely forwarding the ip it is given and thus allowing only one device to connect to it. It is not acting as a dhcp server in it's own right. Can you access the router config pages? I think you want to have a look there and probably make some changes. If everything looks ok there, try hitting it with a hammer. Or maybe see if it has a reset button on the back and configure it again from scratch, the settings it's showing you are not necesarily the ones it is using (probably safer than the hammer option but less fun).