I took spam2004 at turniton dot dk example and made it a bit better. Maybe my setup was a bit different but either way here is how I added a group in Microsoft Windows Server 2003.
<?php
$member_array = array();
$member_array[0] = "cn=user1,cn=Users,dc=yourdomain,dc=com";
$member_array[1] = "cn=administrator,cn=Users,dc=yourdomain,dc=com";
$addgroup_ad["cn"] = "testgroup";
$addgroup_ad["samaccountname"] = "testgroup";
$addgroup_ad["objectClass"] = "Group";
$addgroup_ad["description"] = "Yep just a test.";
$addgroup_ad["member"] = $member_array;
$base_dn = "cn=testgroup,cn=Users,DC=yourdomain,DC=com";
ldap_add($ldap_conn,$base_dn,$addgroup_ad);
?>
Take care and good luck,
Chad R. Smith