iCal is a calendar app that bundled within Mac OS X. I use iCal on my MacBook, and also synchonized the calendar with iPhone. Facebook has calendar feature called "Events" that contains schedules of all events from your friends. To check the calendar, it can be done through the web. But, it is not practical for some users. If you feel more comfort to check Facebook Events within iCal on you Macs, follow these steps.
First, jump to Facebook website and log your account in. Click "Events" menu on the left column, or go to URL http://facebook.com/events. Scroll to bottom of page, and find "Export" option.