Finally, it works!!!
We have spend a lot of hours (read days

), but there is now a new Alfresco Zimlet that perfectly works on 2 of our Zimbra 6.X servers.
I think it also works on the older 5.X Zimbra, but we have tested that yet.
I send a message to yqu (topicstarter) to share our code with (also on the google svn project). We will keep you updated about that!