How to Message multiple PC’s

I have a need for softwrae that will enable a user to send messages to a number of other users/PC’s, and that message to display on a discrete portion of the screen.
The display should not interrupt current work but should be large enough to be easily visible by the user.
The message will be short, and I’m thinking of something like a ticker tape display, or a small text box in the corner of the screen.
Environment is Windows 2000 (active Directory)and a mix on 2000/XP desktops.
Does anyone know of/use such a tool? An msi would be an added bonus.

Thanks for your help,
Alan