Don't forget that some DSL modems will not do log-in when in Bridge Mode.
If you have not set your modem in Bridge mode already, call AT&T and they will talk you through it.
I have Motorola's (one is a spare) and when set to bridge mode my 655 does the log-in.
For AT&T, I skipped the 655 Install CD, and went to the router log-in page (192.168.0.1 - via Browser) and selected the "Manual Internet Setup" page.
Then entered the required information.
Internet Connection = PPPoE
Mode = Dynamic
User name = (Full AT&T user name - includes the @att.net or whatever)
Password = your AT&T Password.
Reconnect Mode = Always On
That will get you connected to the Internet.
Remember to set your wireless security settings and for peace of mind, change your 655 log-in password to something unique and that you will remember.
If you need more help, just ask.