All Windows 2000 domains are also Kerberos realms. However the realm name is always the all uppercase version of the domain name. There is no way to have a Kerberos realm name that is different from the domain name.
Because the Windows 2000 domain name is also a DNS domain name, the Kerberos realm name for the Windows 2000 domain name is always in uppercase letters. This follows the recommendation for using DNS names as realm names in the Kerberos V 5 protocol document (RFC-1510). This only affects interoperability with other Kerberos-based environments.