From Mac Guides
AppleTalk is a legacy networking protocol from pre-OS X days. AppleTalk has had varied support in different versions of OS X. In Tiger, AppleTalk for file sharing is only supported over TCP/IP while AppleTalk for printers is still fully supported.
In OS X, AppleTalk can only be active for one network port at a time.
Appletalk, before the standardization of Ethernet cable networking, was a proprietary means of communication between networked computers, that was based on a "Token Ring" protocol where the network would pass around a "Token" that could be used by a computer to communicate with another computer, and when finished release the token back to the network. This is different from Ethernet, which is more "Chaotic" in the sense that each computer simply waits for a momentary break in communication to put it's data packets into the network. Each computer recieves the traffic, but ignores the data unless it is addressed to their IP #.