Manually configure iCal(Mac OS X 10.5) Use this as Account URL:
http://mail.fmht.net:8080/caldav
Note: Since manual configuration does not allow setting of certain features such as completion of attendee names, it is recommended to use auto-configuration.
Download Kerio Sync Connector(Mac OS X 10.4.11 and later) Two-way synchronization of your calendars and contacts between iCal and Kerio MailServer.