Hoary out of the box doesn't include Libkadm55 and, as far as I know, it isn't contained in any of the standard repositories. So for the Hoary package of Libkadm55 (1.3.6-1), go Here to download it
Ensure it is verison 1.3.6-1 and at the console type...
Then follow the rest of the very good HowTo as referenced in the previous posts. Just got it working on Hoary with it authenticating to a Win2k3 domain, and I am *very* pleased with it / myself.
sudo dpkg -i [Path to deb]/libkadm55_1.3.6-1_i386.deb'
Btw - By default in Win2k3 a "normal" user can join up to 10 machines to the domain without the admin granting special rights. So when asked to provide a username / password combo, and assuming you haven't joined a machine to the domain before, enter your username / password and you should be away.