Here’s how to install drivers for your Atrix 4G on Windows:
Download Atrix 4G Driver For Windows 64-bit systems
Download Atrix 4G Driver For Windows 32-bit systems
Unzip the file then run the .exe file.
After you install the Atrix 4G drivers, put your Atrix 4G into Debugging Mode by going t to Settings->Applications->Development then checking Debugging Mode.
Connect your phone to your computer and open up Device Manager.
You will see Atrix 4G with an exclamation mark, just double-click on it, Update Driver->Browse my computer for driver software->ADB Interface then choose Motorola, then choose Motorola ADB Device.
And you should be good to go.