On the print server, open the Printers (or Printers and Faxes) folder.
Click File, Server Properties and select the Advanced tab.
Here you can turn on and off various logging and notification options.
If I understand correctly, this is a per server setting only.
Another option is to disable the "Messenger" service (not to be confused
with the Windows Messenger instant messaging client) on the client
computers; this will have the side affect off preventing the client
computers from receiving any messages sent via the "net send" command or