I just had purchased an AirPort Express and I have been having trouble configuring it to work in unison with my AirPort Extreme Base Station.
After all the attempts of trying to get the AirPort Express, the AirPort Extreme is at default settings. (Apple Network f17b8a) The problem now is that the AirPort Extreme Base Station is not appearing in the AirPort Admin Utility, yet I am able to connect to the Internet and see the Extreme Base Station in the Network Connections field. This happens to be the case when the Ethernet cord is plugged into the LAN line. (Meaning, I am able to see both the AirPort Extreme and the AirPort Express in the Admin Utility post Soft Restore of the Extreme Base Station when the Ethernet cord is NOT plugged in.)
(I have upgraded AirPort for Mac to version 4.0.1 as suggested via: software update.)
Would anyone have any insight as to how to get my Base Station to appear in my AirPort Utility Admin and get the AirPort Express to work in unison with the Extreme Base Station?
Note: When the AirPort Setup Assistant is run it informs me to use the AirPort Utility Admin, as it doesn’t support configuration of Base Stations not running on Automated DHCP, however as far as remember it was configured to use DHCP. (See attached picture.)
Note: When the AirPort Express Assitant is run, it informs me that it cannot communicate with the Extreme Base Station. (See attached picture.)
Available Networks: (Extreme present, Express absent)

Empty AirPort Utility Admin:

Error Encountered During Base Station Set-Up:

Error Encountered During Express Set-Up:

I’d appreciate any insight. Thanks.
P.S. You can see photographs of the packaging and stuff, if you haven't already at: http://homepage.mac.com/michael.baran