US Robotics wireless router problem

Hi!

I'm trying to set up a small wireless network in my house.
I've a Dlink DSL 320T Ethernet ADSL2+ modem and a USR 5463 wireless router.
Internet works fine when I connect to the model through a lan cable.
when I connect through the wireless router it still works fine but as soon as one of my roommates connects there is an IP conflict. The router assigns to everyone the same IP. I've tried to enable and desable the DHCP server but with no results.

Can anyone please help or I have to buy a new router???
Thank you!!