In XP there was NetSend but it's gone in Windows 7. They have msg.exe but it is not the same. Using PowerShell can you send a true broadcast message to all machines? I have a PS script that runs msg.exe against every machine in a .TXT file but it takes 1 hour to complete and it's no use to us.
Or can PS broadcast a message to a subnet? So every machine on the subnet gets the message at the same time (or within a few seconds)?