in Moodle 2.4! External calendars (such as Google Calendar, or a calendar from another Moodle site) can be imported into Moodle's calendar via the iCal standard.
To import a calendar via .ics file or URL,
- Go to Navigation > Site pages > Calendar
- Click the button 'Manage subscriptions'
- Give the calendar subscription a name and either enter a URL or upload an .ics file
- Click the Add button
A user who has permission to add course or group events, such as a teacher, can import a calendar and create course or group events.
Similarly, a user who has permission to add site events, such as an administrator, can import a calendar and create site events.