Kolab in debian etch

Hello, I have a server running under Debian etch. I need to install kolab, but I can't because:
apt-get install kolabd
->kolabd: Depends: kolab-resource-handlers but it is not going to be installed
apt-get install kolab-resource-handlers
->kolab-resource-handlers: Depends: libapache2-mod-php4 but it is not going to
be installed
apt-get install libapache2-mod-php4
->The following packages will be REMOVED:
  horde3 imp4 kronolith2 libapache2-mod-php5 mnemo2 nag2 php5 turba2

So I can't use horde and Kolab!
Is there any way of doing it? Or it's a developers job?

Thank you!

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