To take this one step further you can automate this -
Once you have followed the Get Started with CalDAV steps here http://support.google.com/calendar/bin/answer.py?hl=en&answer=99358#ical
- Open Apple iCal
- In the toolbar, click Calendar, then Preferences
- Click the Accounts tab
- In the accounts pane on the left, click the + button to add an account
- Enter the following information:
- Account Type: Google
- Email Address: Enter 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.
- Password: Enter the password for the email address you listed above.
Log into iCal
Select Preferences > General
Change your default calendar to your Google/Gmail calendar and voila!
You will have to manually update any existing appointments (you will probably see them in green at least I do) but any new appointments will auto sync without having to select the calendar option
To update your existing appointments so they sync up with Gmail
Click the appointment, select Edit
Beside calendar change it to Google (mine is preset to 'Work' so yours might be too.)