New router – DNS problem!

I have recently switched from using a straightforward hub to a router/gateway. I have installed a domain controller w2k03 on the same 192.168.x.x subnet as the router no problem. It is configured with its own IP address as preferred DNS server, and connects to the gateway and Internet with no further configuration

The problem i have is joining other computers to the domain. I am not sure what addresses they should be configured with. I point them at my domain controller but they receive error “domain controller could not be contacted”. They are configured with the default gateway of the router and i realise that the router has no idea of my dc’s ip address, but dont know how to resolve. Does any body else please?