Time capsule not working with Motorola AT&T modem

I am having difficulty setting my my time capsule, using the airport utility. I have gone into advanced settings on the modem and changed it to share a public IP address, and them I am trying ethernet with the shared address to no avail. What am I doing wrong?

If it's a 2wire router, it's a pain. I can't even make iTunes sharing work properly if it goes through the router. If both computers are on a switch together, sure. If it goes through the router, though, it's a no-go. I've seriously considered turning off the WiFi router in our 2wire and just plugging in my old Linksys router. Just because it's that much of a pain.

I'd recommend going back into the modem and put it back as it was to begin with. You shouldn't need to make any changes at the modem from where it was when you were connecting your computer directly to it instead of to the TC.

Then open up Airport Utility and go through the wizard instead of trying to set it up manually.