The current verson of IM must be enabled in the whole site and on each course... in addition the teacher of each course must enable the IM malbox (because not all courses require separete mailboxes...) Right now all students enrolled must be added to the IM users list in the main course and in each course by IM administrators... this will disapear and all users will have automatically access to IM if IM is enabled...
If you have more questons we can discuss it in spanish by email... or in the spanish course forums... post at any IM thread and I will drop by ;)
Marc