For Joomla 2.5:
Go to Extension/RaidPlanner on your Joomla administration interface ( administrator/index.php?option=com_raidplanner ).
Press the Options button on the upper right corner. Click on Permissions tab. And set View Calendar Privileg to the group who needs to see the calendar.
For Joomla 3 its called Components/RaidPlanner, but same Options button on upper right corner.