Users authenticated with Basic authentication must log on with a valid Windows NT user name and password. The user name usually includes a domain name, in addition to the actual account user name, which identifies a computer or group of computers administered by your Web server as a single entity. For example, a user account called PhilSpencer on the Sales1 domain would log on as Sales1/PhilSpencer. However, you can configure your Web server to assume a default logon domain for all users authenticated with the Basic method, who do not explicitly provide a domain name.
To set the default logon domain