Preventing other network users installing Remote Desktop 3 via the AppStore
How are they supposed to know the login credentials for the other machines? And if they do know the credentials, they could probably do whatever they want with ssh, vnc, afp, etc… anyway, so no need to prohibit ARD, really.

To make it more precise: if you cannot trust your users not to spy on each other, don´t let them know each others passwords!