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 ...

My roommate (Joystickit here on Ars) and I have had a lot of conversations just by utilizing the NET SEND command. Often times it's because I want to talk to him in the next room over and I'm too lazy ...