This is probably the most difficult portion the the setup. The reason the this document currently only covers Red Hat 6.1 is the availability of a pam_ldap RPM. This package is pam_ldap-36-1.i386.rpm. The home page for the current maintainer of the pam_ldap module is http://www.padl.com/pam_ldap.html. A compressed archive file of the source is available here, currently the file is pam_ldap.tgz and expands into a pam_ldap-42 directory.
In order to compile the pam_ldap module you will need the LDAP libraries. The documentation provided with the source recommends the Netscape LDAP C SDK, which is available from Netscape's developer website http://developer.netscape.com. I could not get pam_ldap to compile with this code. I also tried the Open LDAP development package, with which the pam_ldap Makefile has options for compatibility. The only package that seemed to work for me was a CVS download of the LDAP package from http://www.mozilla.org. Hopefully some light may yet be shined upon this module. If you compile the pam_ldap module yourself, you will need to create a configuration file, /etc/ldap.conf. This file is provided with the RPM file. I highly recommend use of the RPM unless you are brave at heart and have plenty of free time.