UPDATE:
After further testing, it appears one can access/sync to the personal calendar. There is no need to create a new shared calendar. It's all in the options used for sharing the calendar.
If you use Zimbra 5.0, you can use Kontact to access your mail via standard IMAP; the global address list via standard LDAP, and your personal and/or shared calendars via standard iCal.
To have read-write access to a Zimbra calendar (this applies to any calendar, whether it be your personal calendar, or a shared calendar), you need to:
- login to the web client (AJAX interface)
- go to the Calendar tab
- right-click on the calendar you want to access and select Share
- select the second option, for external users (view only)
Then, in Kontact:
- open the calendar section of Kontact
- click the Add button under Calendar resources on the left
- select "Calendar in Remote File" option
- give is a name like "Zimbra Calendar"
- enter the Download URL:
http://zimbra.sd73.bc.ca/home/<username>/<calendar name>/ - enter the Upload URL:
http://zimbra.sd73.bc.ca/home/<username>/<calendar name>/ - set the "Automatic Reload" options
- click OK
You now have the ability to create entries in the web client and view them
in Kontact, and to create entries in Kontact and view them in the web
client.
Be sure that your timezone settings in Kontact (use Settings -> Configure Calendar, not Settings -> Configure Kontact) are correct, or the entries will not appear in the right timeslots.
To sum it up, with Kontact, you have access to the following areas of the Zimbra server:
- your mailbox hierarchy (haven't tested how/if tags show up via IMAP)
- the GAL
- if you subscribe to the Contacts and Emailed Contacts folders via IMAP, you can browse through the vCards for your contacts, although Kontact will not auto-complete based on these entries
- any and all calendars that you can access via the web client, by adding a separate calendar resource into Kontact for each calendar
- the documents and briefcase areas are accessible via the webdav kio-slave and any file manager that support kio-slaves
If you enable the "Groupware Resources in IMAP Folders" feature of Kontact, you can also gain proper access to your Tasks, Notebook (Journal), and Contacts. However, Kontact complains about not being able to find a folder called Calendar and will complain about this everytime it checks for messages.

So very, very close.
Cheers,
Freddie