New AT&T Supplied Motorola Modem/Linksys Router Connection Problem

For years my Linksys wireless G broadband router connected to my Linksys cable modem worked just fine. I changed over to AT&T DSL and their Motorola phone line modem won't connect to my router useing the router's internet jack. If I plug the modem's internet cable into ane of the router's 4 network ports, it works, but I use up one of my 4 ports. Can I fix this?
Thanks, De

Lyleb, Thanks for the reply. AT&T was less than helpful & told me to call the router company. I told them to "kiss off" and to cancel the account and send me a shipping lable to return their stuff. My cable company gave me a $29 deal, for a year, so I'm back w/linksys modem & router that work great.
Thanks, again. Later,,,,De