A nifty trick to make messages pop up on the screens of Windows users on your network. Just type the following into the terminal:
smbclient -M NETBIOSNAME -U FROMNAME
The -U FROMNAME part is optional but it adds a nice touch to the message. The NETBIOSNAME is just that. It is NOT the DNS name of the computer (although on some networks it can be).
After you make a connection you type your message, press return and then control-D. It will immediately appear on the screen of your targeted Windows user.
The advantage to doing this from a Mac (or other *nix box) as opposed to a Windows PC is that you can specify the "from" user, which I don't *think* you can do from Windows.
Please use responsibly.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031204021659307