Hi Mahmoud,
Actually it's not recommended to install on the desktop edition of any OS. Even if all the dependencies are there, you wind up wasting a lot of processor and memory resources for the GUI and other goodies, that could otherwise be dedicated to processing mail.
You ought to try your install on the Ubuntu Server LTS (Long-term Support) distros. It's in development for Ubuntu 8 Hardy Heron, and there are some beta builds available
here, or you can stick with the GA build from our normal downloads and install it on Ubuntu 6.06 LTS on the
Zimbra Downloads Page.
Particularly for the latter,
this wiki may be of service as well.
Well, the wiki would help except that a change in Yahoo!'s wiki software has temporarily broken the file. You can find it (mostly, tho not fully updated) at this post