What? If I have OCS why would I want to do this. Some schools are deploying OCS for Audio/Video Conferencing and for web conferencing but don’t want IM. I looked at the group policy template for OC and I can’t disable IM from there but I did find this article http://support.microsoft.com/kb/954648/
and it can be done. So if you need to please follow the steps in the KB. The registry entry needed for this is:
Add new DWORD DisableIM and set value to 1.