Check your AppleTalk network settings (System Preferences -> Network -> AppleTalk) and make sure that it's only enabled on one interface.
Mac OS X ensures that AppleTalk only runs on a single interface whereas Mac OS X 10.1.x let you enable it on multiple interfaces.
It may be that when upgrading to Mac OS X 10.2, the system turned off AppleTalk on your primary network (it doesn't know which NIC you want it enabled on).
Mac OS X ensures that AppleTalk only runs on a single interface whereas Mac OS X 10.1.x let you enable it on multiple interfaces.
It may be that when upgrading to Mac OS X 10.2, the system turned off AppleTalk on your primary network (it doesn't know which NIC you want it enabled on).