Hi, I have a working set on notes for a Zimbra install on a minimal ClearOS i'll post it on the discussion board above, then maybe with a bit more time / testing we can flesh it out into a howto. I managed to break my Zimbra VM install (more specifcally it's LDAP backend) when I tried to change the hostname and haven't had time to investigate why yet...there is something not quite right there but otherwsie I can confirm it installs relatively easily :)
The trick is ensuring that all related ClearOS services are disabled or not installed prior to installation
Tim and I are working on integrating it. It seems that we'll have to work with a clean install - meaning nothing reinstalled when we work with Zimbra. Since Zimbra uses the same service as ClearOS, we'll have to figure out way to install it without installing any of the same features on ClearOS first.