Two days later than promised in the revised roadmap there is finally an "intermediate" release of Horde 4 for Kolab ready. With "intermediate" being the euphemistic word for "while it contains the dynamic calender that one is still pretty broken".
To install the release on a Kolab-Server-2.2.4 system the following commands should suffice:
wget http://files.pardus.de/horde4-20110224.sh sh horde4-20110224.sh
The usual warnings that went with the first Horde 4 release for Kolab apply for this release as well: Do not consider doing this on a productive server. This is just an early preview. And if you want to be able to see anything useful in the added calendar application you should ensure the user you log in with already has a calendar folder and has some data in it.
The state visible in the calendar frontend does not do the changes that happened in the backend any justice. But it can't be helped at the moment: While the Kolab backend for Horde is now largely complete the connection to the various Horde applications still need to be adapted to the changes in the backend.