Here is how you install the owncloud server version on your osx server. I am using Mountain Lion right now.

1. Make sure your web server is working by going to http://localhost/
2. Download the Community Edition at http://forum.owncloud.org/. You will need to click on a few links to get there. My version is 5.0.4 at this time.
3. Then untar: tar -xvf owncloud*.tar.bz2
4. Then copy the folder owncloud to your web file directory. Mine is at /Library/Server/Web/Data/Sites/Default/.
5. Then change ownership of this folder: sudo chown -R _www:_www owncloud
6. Then restart your web server.
7. If all goes well, in your browser, go to http://localhost/owncloud/, it should ask you to input a new admin user/pass. (Copy this down for your owncloud client to sync!)
8. Then you should be good to go. Now try setting up your owncloud client. 😉