Question : stop chatting on clients

i am using a domain controller having windows 2000 server and 100 clients having windows 2000 professional. i want to restrict users on the LAN to use msn and yahoo messengers and other chatting sites. i also want to restrict users to use net send messenger service to send messages to one another, i don't want to disable messenger service on each client computer, i want to controll it by some group policy of active directory,thanx in advance.

Answer : stop chatting on clients

OK the line above basically removes the messenger client from 2K and XP