The problem is in get_plat_tag.sh
To install zimbra under feisty replace get_plat_tag.sh in the installation bin/ directory with this:
#!/bin/sh
echo UBUNTU6
run install and check all prerequisites. Use apt(itude) to install all required packages if necessary.
Before installing, open a second shell in/to the server.
After the zimbra-core package has been installed, immediately go to the second shell and change to /opt/zimbra/libexec. Either copy bin/get_plat_tag.sh from the installation dir here or delete the original and edit it to resemle the above script.
Now the internal "installed" check will return ok and installation will continue without problems and zimbra will run without problems.
Remember: This is not a supported installation
