Publishing calendars with iCal: "Keeping friends and family informed about your schedule is easy when you use .Mac and iCal to publish your calendars to the Internet. To publish an iCal calendar:
1. Select a calendar from the list on the left side of the iCal window.
2. Go to Calendar>Publish… in the menu bar.
3. In the sheet that drops down, enter a name for your calendar.
4. Select your publishing options and click the Publish button.
Your published calendar’s URLs will appear in a dialog box, and you can send them to others"
(Via .Mac Tips.)