ATT UVerse 2 wire gateway connection with Apple Base Station

You just need to connect an ethernet cable from one of the LAN <-> ports on the 2wire to the WAN (circle icon) port on your Apple base station and configure as follows:

Hard Drive > Applications > Utilities > AirPort Utility
Click Manual Setup
Click the Internet icon in the row of icons at the top of the setup page
Look for the setting at the bottom of the page for Connection Sharing and set this to "Off (Bridge Mode)".
Click Update

If AirPort Utility does not "see" the base station when you try to configure it using wireless, temporarily connect an ethernet cable from your computer to one of the LAN ports on the base station. Once you have it configured, you can remove the ethernet cable.

Please post back on your progress.

Is this a dual band AirPort Extreme (AEBS) that you have or an older single band device? Since you posted in the AirPort Extreme 802.11n forum, I assume that you have an "n" capable AEBS.

300Mbps is about the theoretical limit for 802.11n only 5 GHz. If you are in the same room as the AEBS, within 20-30 feet of the router you may see 200-270 Mbps. But, the higher frequency 5 GHz signals are absorbed by walls, ceilings and any obstructions much more quickly than 2.4 GHz signals, so your results will depend on a number of different factors.

Post back on your progress and we'll try to get you as much speed as possible. But bear in mind that in return for speed, you must give up something with 5 GHz and that is distance and penetration power.

On your Mac, hold down the "option" key when you click on the Airport icon at the top of your screen. Information about your current connection will be displayed.

If you are connected at 5 GHz, you will be on a higher numbered channel 149-157, for example and "5 GHz" will be displayed next to the channel.

Look for the Transmit Rate number to get a read on the current bandwidth capability of the network. A Transmit Rate of 220, for example would mean that your wireless is currently operating at a capacity of 220 Mbps.

The "g" network that the 2 wire is transmitting will probably show a 54 Mbps Transmit Rate.