Sorry for the probs, sure you must be tired of fighting with it, but I'd like to say unless you do something stupid, zm just installs (especially on redhat or cent) and runs - but since I don't want a flame war, I won't say that...
I've been running Opensource Zim for several years, and you WILL find it's a great and stable replacement for Exchange... And it doesn't require the nearly constant "dorking with it" that many people "enjoy" when using Exchange..(!)
On Cent, I have to add a couple of deps, to get it to install, but the install script tells you what it needs, and then (get your hosts file and dns right) you should have smooooth sailing.
Peace