So it looks like it is running, but I've never used it so I don't know how to open a dialog window. Moodle is an elearning package that allows a group to collaborate and learn, so I figured it has an internal messaging system. Perhaps overkill for what you want to do.

Perhaps there is a hot-key to bring up a dialog box? Try Control-L or Control-M. Control-L will bring up a URL box in Firefox and open a location on the Desktop, so don't use that.

Viewing their support forums is not encouraging:

http://lanmsngr.sourceforge.net/forum/viewforum.php?f=6