Trying to install Airport Express kills wifi to all devices

[wlow3]

I changed the wi-fi security from WEP to WPA2 on my parents Westell 327w (802.11g) and I updated their iMac, iPod touch and their iPad. All good. Then I get a call from them that the light on the Airport Express (AE) is staying yellow. Crap, I forgot to change that. So next time I'm there I unhook the Ethernet cable from the iMac and plug it into the AE and use the Airport Utility to change the security setting (first I reset it). It gets to the point where it is updating and it seems to be taking forever and I happen to look at the iMac Airport menu bar icon and it shows what I interpret as a dropped connection (no bars) (the iMac was on wifi since I was using the Ethernet cable for the AE). Airport Utility reports an error of some sort and wants me to restart it. Every device -- iPad, iPod touch, iMac -- does not connect because they no longer recognize the WPA2 password. I put the Ethernet cable back into the iMac so I could use the web interface for the Westell and after an hour of deleting settings, hitting forget connection, and disabling and re-abling WPA2 security somehow I got wifi going again. Then I decided to try the old AE again. Same thing happened all over again. UUUUGGGGHHH!!!!! Please, for the love of God, can someone tell me what is happening? Sometimes the Westell drops connections (like to the iPad) but usually turning it off and on restores it. Maybe it just dropped by coincidence as I was updating the AE but I've never seen all devices not recognizing the WPA2 password. Does anyone have any idea what is going on? Thanks.