From the menu, Choose Calendar > Subscribe.

In the following box type:

Subscribe to:

Type in the address of the calendar that you wish to subscibe to using the prefix webcal:// in place of http://. See the following sample for the parts of the address. Use slashes between each section, ending in the name of the calendar followed by .ics

Sample Address:

webcal://(IP number of server)/(folder for Calendar sharing)/(name of calendar).ics  

Example: webcal://196.196.0.1/AnySchoolCal/testcaledar.ics

Subscribed calendar should appear in your iCal.

Find shared calendars at the Apple iCal website.