I would suggest that you start by performing a complete power recycle of your networking equipment. I would also choose the option to perform a "factory default" reset on the AirPort Express Base Station (AX).
One done the AX should broadcast an unsecured wireless network with a Network Name of something like: Apple Network NNNNNN. Can the WinXP laptop find and connect to this Wi-Fi network now?
Thank you SO MUCH Tesserax for taking the time to help!
I powered everything down, slowly powered everything else up from the modem to the airport then the computer. I then reset the airport & rescaned it through utilities. I set up a new network & voila! wireless up & running again.
I am going to try to connect the laptop to the network now.....well, mabey tomorrow night, I've had enough for 1 evening!
I will update....or possibly be begging for more help...we'll see!
Thanks again for your time!