Sebastien Tricaud sent us some patches to allow the communication between OSSEC and Prelude. If you are a Prelude and OSSEC user, please check it out and let us know how it goes.
Instructions on how to set it up is available at our FAQ entry How to enable Prelude Output? and at this link.
You will also need to use our latest development version from http://www.ossec.net/files/snapshots/ossec-hids-071006.tar.gz