I have a at&t dsl wireless modem and built in router.

I have a at&t dsl wireless modem and built in router. I need to add linksys or camcast router to have another ip address set up to connect to my laptop? How can I configure this? what will happen to my modem ip address if I configure linksys or camcast router to a new ip address. can I use both one for the dsl and one for the other ip address. please guide me. thanks