When you talk about the bt voyager adsl router, do you really mean the adsl modem? If so, you need an adsl modem+router in one (or just a modem with ethernet output).
then you could either just use the modem+router in one to connect all your computers, or if you have more than that you could get a switch and connect that to one of the ports on the router to extend it.
if you just have an adsl modem with ethernet output, then you can connect that to the router you have, and then all your computers to that router.