Forgot password for Airport Express can you help?

Try using something like a straightened paperclip or tip of a ballpoint pen to press and hold the reset button for one or two seconds - that will reset the Airport Express.

This from page 40 or thereabouts of the AE user guide:

Chapter 5 Tips and Troubleshooting
You Forgot Your Network or AirPort Express Password
You can clear the AirPort network or AirPort Express password by resetting AirPort
Express. Follow these steps:

1 Use the end of a straightened paper clip to press and hold the reset button for one
second.

2 Select your AirPort network.
-On a Macintosh, use the AirPort status menu in the menu bar to select the network
created by AirPort Express (the network name does not change).
-On a computer using Windows 2000 or Windows XP, hold the pointer over the wireless
connection icon until you see your AirPort Network Name (SSID), and choose it from
the list if there are multiple networks available.

3 Open AirPort Utility (in the Utilities folder in the Applications folder on a Macintosh,
and in Start > All Programs > AirPort on a computer using Windows XP or Windows
2000).

4 Select your AirPort Express and click Configure.

5In the dialog that appears, make the following changes:
-Reset the AirPort Express password.
-Turn encryption on to activate password protection for your AirPort network. If you
turn on encryption, enter a new password for your AirPort network.

6 Click OK.
AirPort Express restarts to load the new settings.

You're welcome!