BTW, to uninstall, make sure you follow these directions:
Uninstalling Zimbra on Mac OS X - Zimbra :: Wiki
They should work for Leopard as well.
Here's a short version.
Open Terminal.
Do
sudo -s (or do
sudo su -, same thing).
At the prompt, enter an administrator password.
Make sure that opt/zimbra/libexec/installer/install-mac.sh exists.
At the root prompt
cd /
/opt/zimbra/libexec/installer/install-mac.sh -u
Then look at the wiki entry and read the section on Remaining issues.
Once you've properly uninstalled Zimbra, you can reinstall it, starting with running the installer off the .dmg image.