You can use group policy (either local or with a GPO in a Windows 2000 Active Directory) to remove Run from the Start menu and disable the command line. You can also disable the messenger service on each machine. If you have a Windows 2000 AD domain, it would be easier to create a GPO and apply it to either the domain or the OU with the students' accounts. Start>Run>mmc. Go to the Users Configuration>administrative Templates> Start Menu & Taskbar to remove Run from the Start menu. Go to User Configuration>Administrative Templates>System to disable the Command Prompt. That way, the students can't access the command line. Either method will prevent them from using netsend.