Sounds like you still have a conflict going on between Zimbra and Apache. I've installed Zimbra a few times on clean minimal installs of CentOS 5.2 and never had an issue.
From how Zimbra is setup it seems to me that it should be viewed as more of an appliance, than an application that you install alongside other applications. This is no different than how Microsoft recommends Exchange to be installed.
To get around all this I use VMware, but Xen with paravirtualized guests would probably work even better. I have a guest for LAMP and a guest for Zimbra. I use the reverse proxy module in Apache to get around only having one static IP. |