I have installed a trial of Zimbra on a 10.4.11 box and configured my Leopard workstation to use the iSync Connector.
I made it create a new CALDAV account in iCal and was able to sync my calendar flawlessly..
I did however notice that the Tasks did not sync...
I am curious how the implementation of Task syncing works with the Mac as opposed to it seeming to work in Outlook.
I did see another post regarding Task syncing in version 5..