http://www.googletutor.com/2008/02/19/easy-wordpress-and-google-calendar-integration/
http://code.google.com/p/wpng-calendar/
The Wordpress Google calendar plugin allows for the integration of a Google calendar into a Wordpress blog. This section describes how to install the plugin and get it working.
1. Request Google GDATA API key (see link below)
2. Upload the contents of the ZIP file to the /wp-content/plugins/ directory
3. Activate the plugin through the Plugins menu
4. Configure your GDATA API key in the plugin options panel
5. Configure a Google calendar in the plugin options panel
6. Configure the option to render the description field as Wiki markup
7. Create a page and add the ’show-wpng-calendar’ custom field with the number of weeks you want to be displayed
8. Add the widget to your sidebar and configure the title and number of events to display