There are currently 3 known sources with instructions how to install Horde as the web client for Kolab:
- The official documentation, which hasn't been updated for a while.
- Some additional instructios in the Kolab wiki.
- The folks at the Calgary Linux User's Group did a workshop on installing Horde and Kolab, and put together a good start. Their webpage is http://www.clug.ca/node/359, and I've taken the liberty of attaching their handout PDF to this page as well.