A. A. Ensure the "Messenger" service is started
(Control Panel - Services - Messenger - Auto). To send a message type:
c:> net send <machine name> "<message>"
Or instead of a machine name type * to broadcast to all stations
There are also various GUI utilities, and one of the best is NT Hail at http://www.geocities.com/SiliconValley/Bay/1999/NT_Hail.html