You are going to want something like:
$conf['authtype'] = 'ldap';
$conf['auth']['ldap']['server'] = 'auth.metu.edu.tr';
$conf['auth']['ldap']['binddn'] = '{username}@{yourdomain}';
$conf['auth']['ldap']['bindpw'] = '{valid Password}';
$conf['auth']['ldap']['usertree'] = 'cn=People,dc=metu,dc=edu,dc=tr';
$conf['auth']['ldap']['userfilter'] = '(samaccountname=%{user})';
$conf['auth']['ldap']['mapping']['name'] = 'displayname';
$conf['auth']['ldap']['referrals'] = 0;
$conf['auth']['ldap']['version'] = 3;
You may need to change cn to ou in your case.
I don't know a whole lot about LDAP, but that is roughly how I have ours configured. I'm not mapping any groups through LDAP, but rather doing it through the plain text files. More configuration is needed for groups.
There is a lot more information on LDAP here:
http://www.dokuwiki.org/auth:ldap