Can a DSL modem and wireless router.?

We recently just bought a new laptop so we can have wireless in our house. Before that, we only had a desktop PC that has DSL running for internet through a Westell modem provided by AT&T. We bought a Cisco, Linksys wireless router to provide wireless internet to our laptop for around the house. My question is how does my dektop PC still get DSL running to it if I have to use the wireless router ethernet cable running through the DSL modem? Are the extra ethernet ports on the wireless routerbesides the one labled "internet" supposed to be for me to run the ethernet cable to the desktop to provide DSL? So basically I am asking how do i have DSL and wireless when I have to connect the router to the Westell modem's ethernet port which takes away the port that runs to my desktop to provide DSL?