Windows XP SP2 has a feature that causes a balloon window to be displayed every time a print job is sent to a printer informing the user that the job has been printed.
To disable this feature, do the following
The following key needs to be created (or edited) with regedit
HKEY_CURRENT_USER\Printers\Settings
Value Name: EnableBalloonNotificationsRemote
Data Type: DWORD
Value: 0