I had the similar problem with a PB/400, I was unable to select a zone in the Appletalk panel of the Network control panel. Appletalk could be selected but it would not recognize the zones on our network. After re-installing OSX and having no luck in effecting the problem, I rebooted in Classic. Appletalk was fully functional and allowed me to pick the proper zone. When I rebooted back in OSX, the problem returned.
Since reinstalling OSX had no effect, I decided to do a clean install of OS9. After the install and before Classic was run for the first time, I threw out the Appleshare Prep and AppleTalk prefs files (another forum mentioned that these were problematic). I also removed an underline character within the name of the OSX Sharing panel (not sure if this had any effect).
I not exactly sure which item did the trick, but it works now. I had been fighting this problem for over a month (just about the time I installed 10.2.4).
