[Samba] Joining an AD domain without password

[Andreas]

samba-3.0.6, win2k will all patches from windowsupdate as of last
friday

Should it be possible to join an AD domain (win2k) without a password
on the client side if the machine is already created in the ou=Computers
container? I seem to be unable to do this: either "net ads join" will ask
for a password or it will try with the current user's kerberos ticket and
fail if this user doesn't have the right privileges.

This seemed to work with "net rpc join" when win2k is not in its native mode.
Am I missing something?