One of the problems I faced integrating Google Calendar with Joomla! was getting a weeks worth of upcoming events from all different calendars to show up on a module.  The third party extensions were bulky and did not give the results I was looking for.  So, I made my own using the RSS feed from Google, Yahoo Pipes and the Simple RSS Reader from JoomlaWorks. These directions are for US East time zones.  To use a different time zone, you will need to change the Google calendar URL code as well as some of the pipe information.