What I tried was to restore the profile that I had saved just before shutting down and disconnecting everything the other day. My XP guest laptop still wouldn’t get an IP. I tried with a Windows 7 laptop and after authenticating with the AP, BINGO! It got an IP from ZS as expected… So I did an ipconfig /release * then ipconfig /flushdns and turned off the wireless on the XP laptop. Rebooted, turned wireless back on and everything works great! Something must have been “stuck” somewhere, probably Microsoft…
Thanks for everyone’s efforts!