Well, I did some tests on my local networks.  My problem appears to be
that my krb5 (NetBSD) machine is sending packets on udp port 88 ("kerberos",
in /etc/services) rather than on port 750 ("kerberos4").  I noticed that
kinit had a '-S service_name', but this doesn't do what I expected; the
packets still go on port 88.

I also noticed that the requests are all stamped with 'v5'.  I'm wondering
if I've failed to communicate that the kerberos servers in question are all
V4.

I had 
[login]
        krb4_convert = false
        krb4_get_tickets = true
        krb5_get_tickets = false
in /etc/krb5.conf, but it occurs to me that this may only affect login, not
kinit.  How does kinit decide which service to use?

-s