Configuring airport express without wireless computer

Question

I've got a 2008 Mac Pro with no wireless hooked up to the square Airport Extreme by ethernet cable.  The airport extreme serves other wireless computers throughout the house.  Last year, it was complicated configuring 2011 airport expresses to extend my network using the Mac Pro as the home computer, but I finally managed it with the help of an Apple tech who said most other techs would probably not know the trick to doing it.  It worked great for over a year. 
Today, out of nowhere, airport utility came up with an error message and told me I needed to change settings to a LAN bridge.  I followed directions, but the effect was to wipe out all my settings.  I managed to reset and get the extreme back working, but I'm having trouble getting the airport expresses properly configured. Instructions online are based on doing it with a computer that's also wireless.  Part of the trick in configuring involved deselecting a lower button in Airport Utility, then going to areless settings and changing WAN to extend the network. 
I wish I would have gone to the trouble of doing screen grabs with each step along the way, but if anyone knows the steps for reconfiguring the airport expresses using a computer without wireless, I'll pay for your kids' college:  or at least ask God to let you win the lottery. 

Answer 1

A cool Apple tech, realizing that I was only having problems because their software had topedoed my working set-up, actually gave me a no-charge rundown of the standard procedure using that ethernet trick, which seemed to work up until the last step, but at that point, the update and restart of the apple express failed each time I tried.  From what I remember when I initially configured the express last year, the ethernet trick is part of the right procedure.  Thanks.