Sending broadcast messages to client machines in Windows

We are within a library LAN that is connecting to the internet. In the network, there are over 1000 PC machines distributed in around 60 libraries. In each library, there are at least 1 machine (which we called CT) that can be used by our librarian only. Public can use other than those machines. All machines in our network are using Windows XP at this moment.

Our librarians would like to send broadcast messages to the client machines (i.e. used by public) in the library. However, we don't allow our client machines to send messages to CT machines/other client machines, or receive any messages that is not sent from the CT machine(s) in the library.

1) In Windows XP/7, is there any built-in feature that can achieve our goal?
2) If the answer to question 1 is yes, is there any security risk in the network by using that tool?
3) If the answer to question 1 is no, then is there any common third-party tool that can achieve our goal?

LVL 16
Peter KwanAnalyst ProgrammerAsked:
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1) Would this work for you:

2) Not that I can think of if it's already enabled in your environment.

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Peter KwanAnalyst ProgrammerAuthor Commented:
Thanks, but is there any configuration in the client machines (using by public) such that public users does not have the right to execute the command (msg/net send) in their machine? Public users are using a standard user account with no administrator rights.
You could disable the windows messaging service.
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Peter KwanAnalyst ProgrammerAuthor Commented:
I read the msg.exe help, but I have some question in my mind:

If I use msg.exe * to send a message , will users in Library B also receive the message? I would like to limit the broadcast message to be received by that library only  (all libraries are in different IP range).
msg * sends to all sessions on the specified server, could you use a file to list all the recipients?

msg /?
Send a message to a user.

MZ:\>msg /?
Send a message to a user.

MSG {username | sessionname | sessionid | @filename | *}
    [/SERVER:servername] [/TIME:seconds] [/V] [/W] [message]

  username            Identifies the specified username.
  sessionname         The name of the session.
  sessionid           The ID of the session.
  @filename           Identifies a file containing a list of usernames,  sessionnames, and sessionids to send the message to.
  *                   Send message to all sessions on specified server.
  /SERVER:servername  server to contact (default is current).
  /TIME:seconds       Time delay to wait for receiver to acknowledge msg.
  /V                  Display information about actions being performed.
  /W                  Wait for response from user, useful with /V.
  message             Message to send.  If none specified, prompts for it  or reads from stdin.

Peter KwanAnalyst ProgrammerAuthor Commented:
Thanks very much. What we are concerning is that if users logon to 2 machines with the same user name INT001, if we type:

msg INT001 <message>

Then will the user on the two machines receive the message?
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Windows XP

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