You can disable networking event balloon tip notifications by adding a key to the registry:
In there create a DWORD value called "EnableBalloonTips", it will get the value 0 by default, dont change it.
Exit the registry editor then reboot. Networking icons in the taskbar will operate as before (showing connectivity of network/dialup/wireless); however, balloon tips stating connection/disconnection events will no longer be displayed by XP.
Notifications, Balloon Text, Registry hacks, Windows XP