This should help you, this is using command prompt [net send]
NET SEND {name | * | /DOMAIN[:name] | /USERS} message
Sends messages to other users, computers, or messaging names on the network. The Messenger service must be running to receive messages.
You can send a message only to an name that is active on the network. If the message is sent to a username, that user must be logged on and running the Messenger service to receive the message.
name
Is the username, computername, or messaging name to send the message to. If the name is a computername that contains blank characters, enclose the alias in quotation marks (" ").
*
Sends the message to all the names in your group.
/DOMAIN[:name]
Sends the message to all the names in the workstation domain. If name is specified, the message is sent to all the names in the specified domain or workgroup.
/USERS
Sends the message to all users connected to the server.
message
Is text to be sent as a message.
If you want more sumarised version you can go to
http://www.amset.info/windows/netsend.asp
PS, this type of sending is one way and not shown in notepad form, instead it is in a pop up form