The "Talk" feature in the Apple Network Administrator Toolkit requires a Macintosh with dual channel sound capabilities that can record and playthrough sound at the same time.
The "Talk" feature will not work with the systems listed below:
Macintosh Classic
Macintosh Classic II
Macintosh Color Classic
Macintosh Color Classic II
Macintosh SE/30
Macintosh IIci
Macintosh IIvi
Macintosh IIvx
Macintosh LC
Macintosh LC II
Macintosh LC III
Macintosh LC 475
Macintosh LC 520
Macintosh LC 550
Macintosh LC 575
Macintosh Quadra 605
Macintosh Performa 200
Macintosh Performa 250
Macintosh Performa 275
Macintosh Performa 400
Macintosh Performa 405
Macintosh Performa 410
Macintosh Performa 430
Macintosh Performa 450
Macintosh Performa 460 Series
Macintosh Performa 475
Macintosh Performa 476
Macintosh Performa 520
Macintosh Performa 550
Macintosh Performa 560
Macintosh Performa 570 Series
Macintosh Performa 600 Series
Macintosh PowerBook Duo 200 Series
Macintosh PowerBook Duo 2300 *
Macintosh Duo MiniDock
Macintosh Duo Dock
Macintosh Duo Dock II
PowerBook Duo Dock Plus
* Although the Macintosh PowerBook Duo 2300 is able to record and playthrough sound simultaneously, the Talk feature is disabled on this system due to a software issue discovered late in the process.