Do the pop up alerts look like the one in the example shown here
? If so, follow the instructions to "Disable Windows Messenger Service
". The Messenger service is a network-based system notification service service that transmits net send messages and messages that are sent through the Alerter service between client computers and servers. It should not be confused with Windows Messenger which is a proprietary instant messaging client included in Windows XP, 2000 and 2003 Server.