no, it is not a command line utility. winpopup uses a graphical interface. though, knowing microsoft, there may be some command line options that you can send it to use it in non-graphical mode, but ...

I've used Windows Messenger service (or, at least, I think that's what it is) before to send a pop-up/broadcast message to all (or selected) users before, but it's been a while. What's the best way ...