At CEIT we have built a lot of Drupal 6 sites that authenticate users against the UQ LDAP. To achieve this we used the LDAP Integration contributed module and configured the LDAP server settings with a service account that had appropriate search permissions within the UQ LDAP directory.
The UQ LDAP admins had told me that it should be possible to authenticate users without resorting to a service account. This however did not work with the LDAP Integration module and Drupal 6 and I never had time to spend debugging it.
