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In order to successfully sync Google Calendar and Windows Live Calendar, you will need to follow the following instructions to acquire a secure URL to your Google Calendar, and apportion access to this in your Windows Live Calendar.
To begin, open Google Calendar, and browse to Calendar > Calendar settings (via the small cog in the top-right corner) > Calendars > Share this Calendar > Calendar Details.
At the foot of this page is the section marked Private Address. Clicking the ICAL button will reveal a link such as http://www.google.com/calendar/ical/USERNAME%40googlemail.com/public/basic.ics. This address will give you secure access to your Google Calendar from Windows Live Calendar.
Following this, in Windows Live, sign in to your account and then then go to Calendar > Subscribe and in the Calendar URL field paste the link acquired from your Google Calendar.
Note that this method can be used in both the online version of Windows Live and the Vista OS Windows Live Calendar tool.