Thanks Marcus, that sound's promising!
Let me know if there is anything I can do to help but I am not that technical I'm afraid. I know there are some other people on the Forum who would be very interested in what you are proposing too.
At the moment I am authenticating both my Zimbra and Sugar Users through Active Directory successfully and that should work with any LDAP server I guess.
As to the last point, you are asking a complete idiot Marcus!
All I can offer is that there is another Forum on this site which has a slightly similar subject to it. It is about allowing the 'Mailto:' function to access Zimbra instead of your local email client. There is in fact an extension for Mozilla that allows this but it still makes you log on again to Zimbra instead of just bringing up the Compose window.
Don't know if it's any help but have a look here if you want to:
Windows Integration
Good Luck, I wish I could offer more help than just luck but I'm sure there are many others on here who can help! I have found all the Users on Zimbra Forums to be very helpful.
Russ