Hi,
probably the combination of Kerberos and LDAP still lack some functionaltity. I got it to work with a couple of tweaks to the LDAP code and the Apache authentication, see the following discussionin mantis:
http://www.ilias.de/mantis/view.php?id=13356
I had tested those in ILIAS 4.4 and 4.5(beta) which became 5.0 then (and I could see no significant changes to the LDAP and Apache modules sice, so maybe it still works the same way.
Regards
Ingo