Suggest surfing your ISP (Internet Service Provider) Web site and look for support / install instructions. Whether wireless or "wired" connectivity, many ISPs have their recommended configurations for both Win7 and MacOS systems. And, they often show nice pictures of different connection methods with each pros/cons as well.
If wondering, my ISP provided DSL modem is a combo box. re: Its a DSL modem, Router with wired ports (for up to 6 devices) and also does wireless Router connectivity as well. Perhaps your ISP provided you a combo box as well?
I dunno who gave you the modem, but I agree you should do this:
With ATT and some other providers I've used, it's best to then setup the modem, as far as possible, to do nothing but pass traffic on to the router. No firewalls, port forwarding, routing (except to the router) or wifi. Let the Extreme do all that. I have my 2Wire set to do just the minimum, and then use 10.0.x.x addresses from the Extreme. I can then avoid double NAT problems and everything is happier with unicorns and rainbows.