This code is how to send NET SEND messages to all the connected SQL Server users in an NT local area network:

 CREATE PROC notify_users(@notification VARCHAR(100) = 'SQL Server shutting down')ASBEGINSET NOCOUNT ONDECLARE @msg VARCHAR(250)DECLARE @hostname sysnameSELECT @hostname= min(RTRIM(hostname))FROM  master.dbo.sysprocesses (NOLOCK)WHERE  hostname <> ''WHILE @hostname is not null    BEGIN	set @msg='exec master.dbo.xp_cmdshell "net send ' + RTRIM(@hostname) + '' + RTRIM(@notification) + ' "'        EXEC (@msg)  	SELECT @hostname= min(RTRIM(hostname))	FROM  		master.dbo.sysprocesses (NOLOCK)	WHERE  		hostname <> ''		and hostname > @hostname    ENDSET NOCOUNT OFFEND