What do you mean "remote rooms"? Is this for residential? If it is for commerial, get a cabling company in and wire up the remote rooms, or at least get one cable to somewhere near the remote rooms so you can place a 2 wireless router there.
Most wireless routers will also allow a limited number of wired connections. If you get one CAT5 to the other area, you can use that to tie the two together.
I am fairly confident that you can not place a 2nd DSL modem on a DSL circuit that already has a modem. You would need to get a whole second DSL circuit on another phone line, send that phone line to a "remote room", and place a second wireless router on it.