You can subscribe to user and group calendars in iCal. When you subscribe to calendars in iCal, the calendar stored in iCal is read-only. You can't change events in iCal, but when events change on the wiki server, those events are updated in iCal.
If you have Mac OS X v10.6 or later installed, you can add your personal calendars as an account in iCal. You can't add group calendars as an account. When you add personal calendars as an account, changes are synced between iCal and the wiki server. You can change an event in iCal and it'll update the event in the wiki server, or if you change the event in the wiki server it'll update the event in iCal.
To subscribe to a web calendar in iCal:
While viewing a personal or group calendar, hold the mouse cursor over the calendar you want to subscribe to and then click the Information (i) button.
Click "Subscribe in iCal."
In iCal, click Subscribe.
When you're asked to authenticate, enter your wiki account name and password.
To add your personal calendars as an account in iCal:
Open iCal in Mac OS X v10.6 or later.
Choose iCal > Preferences.
In the Accounts pane, click Add (+).
Choose the CalDAV account type and enter the user name and password you use to log in to the wiki.
For server address, enter the URL of the wiki server (for example, wiki.example.com).
If the wiki server uses an external calendar server, you must enter the URL of the calendar server instead of the wiki server. If you can't create an account using the wiki server information, contact a server administrator to find out if your wiki server uses an external calendar server.
Click Create and complete the setup assistant.