Instructions: Subscribe to a calendar using Google Calendar
In Google Calendar look for the Other Calendars block on the left hand side. Click Add and select Add by URL. Now type in the GIXr calendar address. This can be found in the "Downloads for registered users" section of a GIXr calendar web page.
Example: http://www.gixr.com/events/ics.php?gc=3

Instructions: Subscribe to a calendar using Google Calendar