I want to make sure I am understanding what you are wanting. Are you wanting to bring your private Google Calendar into your Zimbra Calendar? Here is what I use for my Google Calendar to show in Zimbra.
http://www.google.com/calendar/ical/...889d/basic.ics
I use this and my calendar shows up just fine. I got this by clicking on the private ical button in Google and just adding that link.
jd