Jason mentions that you can reset the AirPort Express by holding down the tiny reset button. Absolutely true, but it's only one of three ways to reset the device (and each variety of reset does something a bit different).
The three reset types are soft, hard, and factory default. You issue a soft reset when you need to reset your base station password (if you forget the password you originally entered, for example). A hard reset is for those times when the device stops responding. This kind of reset doesn't erase saved profiles. The final reset -- factory default -- does exactly what it says. It returns the AirPort Express to the condition it was in when you pulled it out of the box. Invoking a factory default reset erases all saved profiles.
To perform each reset, follow these steps:
Soft Reset
With the AirPort Express plugged into a power outlet, launch the Network System preference and choose AirPort from the Show pop-up menu. Click the TCP/IP tab and choose Using DHCP from the Configure pop-up menu. Press and hold the device's reset button for 1 second. The light will flash yellow and you'll have five minutes to make changes before the AirPort Express reverts to its previously saved configuration.
Hard Reset
With the AirPort Express plugged into power, press and hold the device's reset button for 10 seconds. A green light will flash for a bit and then the device will reset itself -- a process that takes about 45 seconds. Once reset, you can configure it with the AirPort Express Assistant or the AirPort Admin Utility.
Factory Default
Unplug the AirPort Express from the power outlet and press and hold the reset button. While still holding down the reset button, plug the device into a power outlet. Hold down the reset button until you see the light flash green four times. Let go of the button and the device will reset itself. Wait the requisite 45 seconds and configure it with the AirPort Express Assistant or AirPort Admin Utility.
Double-post ftw
