There are two primary applications using DAV with Zimbra server.

- WebDAV to access mail attachments and Notebook documents in the 
  users mailbox.
- CalDAV to access the calendar appointments in the mailbox server 
  using 3rd party calendar client.

The main DAV URL for users mailbox is

http://<server>/dav/<username>

Most of modern operating system now comes with DAV support built in.  
On Windows XP, File Explorer can be used to access DAV repository.

Start -> My Network Places -> Add a network place

Then Choose another network location.  Type in the main DAV URL.  
The system will then prompt authentication dialog.  Type in 
Zimbra username and password.

On Mac OS X, Finder has built in support for WebDAV.  
Menu -> Go -> Connect to server.  Then type in the main DAV URL, 
click + to add.

Using the WebDAV interface, users can view contents of Notebook and 
Briefcase folders, and also copy files in and out of the folders.  
There is a special folder named 'attachments'.  It's not a real folder, 
but kind of like a view of the mail attachments.  The attachments can 
be browsed based on the date the email received, content type, or by 
the sender.

The second use case is with CalDAV compliant calendar client.  There
are several CalDAV clients available.  Currently  the most popular 
and feature rich client is Leopard iCal.  Zimbra CalDAV has been
tested against the release build of Leopard.  Some of the other
calendar clients that support iCal are Mozilla Lightning, Mozilla
Sunbird, Gnome Evolution, and OSAF Chandler.

iCal supports CalDAV principal concept, and the URL to use is simply

http://<server>

Using the supplied username and password it can discover the user's
calendar.

For other clients, users may need to
add "Calendar" at the end of the URL to point to the calendar
folder.  e.g.

http://<server>/dav/<username>/Calendar

iCal on Tiger and older release only support ics import and export,
not the full CalDAV.  The ics import mode is not compatible with
CalDAV at all, and the usage is completely different.  In order
to use ics import mode, first the user needs to export the 
calendar folder as ics, save to a file, then import the file into 
the target calendar application.  Using ics import mode, the 
changes made to the 3rd party calendar is saved as a local copy, 
and does not automatically synchronize with Zimbra server.  When
using CalDAV client, the changes are immediately saved to the server,
unless the client is run in the offline mode.  There is no manual
file based synchronization needed as with ics import mode.