Network Lan messenger is an inexpensive alternative to public instant messaging for local area networks. If you are looking to deploy IM within your office network, yet avoid going through an outside ISP, such as American Online or Netgear, you should investigate LanTalk NET.
This article explains how to install and use Microsoft Winpopup utility to send messages in your LAN network.
This article explains how to stop messenger spam and disable messenger service or enable it ( a little grey box with adv or a "Winpopup spam" ).