1. Open Apple iCal, go to Preferences and then the Accounts tab.
2. Click on the + button to add an account.
3. Under Account Information, enter your Google Account username and password.
4. Under Server Options, add the following URL:

https://www.google.com/calendar/dav/YOUREMAIL@DOMAIN.COM/user

Replace ‘youremail@domain.com’ with the email address that you use to log in to Calendar. Make sure to include the ‘@domain.com’ portion (which is @gmail.com for Gmail users) in this section.
5. Click Add.
6. Under the Delegation tab, select the calendars you’d like to add to iCal by checking the boxes next to them. You may need to hit refresh to get the latest list of calendars.
7. Add your email address to your Address Book card by selecting Add Email. You’ll be prompted to add your email address only if your address is not already in your Address Book.

It takes no time at all to get iCal and Google Calendar connected to give it a go. The best part about it is that it’s even if you don’t use Google Calendar it’s a great back up!