IIRC, you should be able to at least sync the Calendar & Contacts using the Yahoo! Mail account type; syncing Tasks and Notes are not available yet.
Are you getting a red dot indicator during the sync? If so, please enable debugging as per this article, and send over the <install_directory>/zimbra/zdesktop/log/zdesktop.log file.
http://wiki.zimbra.com/index.php?tit...by_an_error.3F