I thought I'd post my setup so others will not have to work so hard to get an end result.

Upgrade the host OS before install and add the locale stuff (get heaps of problems if you don't):
apt-get update
apt-get install language-pack-en-base
locale-gen en_AU #change to your locale
apt-get dist-upgrade

Too check you locale settings:
locale -a -v

apt-get install libgmp3c2 sysstat sqlite3 # is needed by Zimbra
apt-get install unzip p7zip-full lzop lzma arj zoo cabextract tnef nomarch bzip2 rpm #for unpacking files in emails

apt-get install netcat-openbsd pax #need these as well

Remove all references to Apache and Sendmail via purge or autoremove

apt-get purge sendmail-bin apache2
apt-get autoremove sendmail-cf
apt-get autoremove apache2-utils
reboot #need to do this to flush system memory

Down load Zimbra FOSS and follow install instructions from Zimbra website

You should have a working system.

**Note

If the cpu usage just keeps on going up and the file /opt/zimbra/zmstat/zmstat.out just keeps on growing with Use of uninitialized value $line in pattern match (m//) at /opt/zimbra/libexec/zmstat-io line 69. then the newest PROXMOX (openvz) containers have problems with iostat.

To fix you need and older version of sysstat from the Debian site. I just downloaded from Debian -- Details of package sysstat in squeeze then extracted the file iostat by

ar -x sysstat_9.0.6.1-2_amd64.deb
tar -xvf data.tar.gz
cd ./usr/bin/
then moved the file to - cp iostat /opt/zimbra/
Modified /opt/zimbra/libexec/zmstat-io as root
with

# my $IOSTAT = '/usr/bin/iostat';
my $IOSTAT = '/opt/zimbra/iostat';
if (! -e $IOSTAT) {
# $IOSTAT = '/usr/sbin/iostat';
$IOSTAT = '/opt/zimbra/iostat';

restarted zmstatctl stop then zmstatctl start as su - zimbra