The official site of the MIT Kerberos is http://web.mit.edu/kerberos. There, find links to any other relevant resource concerning Kerberos, including Kerberos installation, user, and administration guides.
The paper at ftp://athena-dist.mit.edu/pub/kerberos/doc/usenix.PS gives quite an extensive insight to the basic principles of Kerberos without being too difficult to read. It also provides a lot of opportunities for further investigation and reading about Kerberos.
The official Kerberos FAQ is available at http://www.nrl.navy.mil/CCS/people/kenh/kerberos-faq.html. The book Kerberos—A Network Authentication System by Brian Tung (ISBN 0-201-37924-4) offers extensive information.