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?