Apache 2.2 changed the way you configure LDAP authentication. mod_auth_ldap was replaced with mod_authnz_ldap, so don't forget to enable the new module and disable the old one. Because I'll always forget, here's the new style config.

AuthType basic
AuthName "admin"
AuthBasicProvider ldap
AuthLDAPUrl ldap://ldap.example.com:389/ou=people,dc=example,dc=com?uid?sub
AuthLDAPGroupAttributeIsDN off
Require ldap-group cn=systems,ou=groups,dc=example,dc=com
AuthLDAPGroupAttribute memberUid

The sections in bold are the sections I had to change from the 2.0 config.