You can use this to send brief messages over a LAN. All messages are encrypted and this program does not require configuration or Internet access. It can be used as a replacement for WinPopup utility.

OfficePopup allows the management team to inform employees about any important events or incidents by sending messages to entire departments or individual users on your network.
By default, OfficePopup allows your employees to send and receive messages. However, in case you would like to use OfficePopup to broadcast messages only, you can specify that during the installation. This way, you can be absolutely sure that particular employees wont spend most of their day sending messages to their coworkers.
Advanced users will find that OfficePopup is a great replacement for WinPopup utility that was supplied with Win9x/NT and is unfortunately missing in the recent versions of Windows such as Windows 2000 and XP.

Being able to send announcements to your employees is crucial to your company's success. Our LAN messengers allow you to inform your personnel about any important events or incidents in a matter of seconds.
Our LAN messenger is compatible with Windows 95/98, Windows Me, Windows NT 4.0 as well as Windows 2000 and XP. It runs on any TCP/IP-based Local Area Network (LAN). The LAN messenger is optimized for minimum network traffic and features an intuitive user interface allowing your employees to spend very little time learning the new software.

The license of this software is Free Trial Software, the price is $34.95, you can free download and get a free trial.