iRedmail Pro - new install confusion

==== Required information ====
- iRedMail version: iRedAdmin-Pro-LDAP-2.1
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): LDAP
- Linux/BSD distribution name and version: Centos 5.6
- Related log if you're reporting an issue:
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I am a bit lost using these install instructions: http://www.iredmail.org/admin_installation_rhel.html

There's no mention of what LDAP to use, what schema, etc.

Following the instructions just does not work and are also wrong, for example : there's no settings.ini, just settings.py.

am I supposed to first install the OSE version and then upgrade ?