Restricting By Hostname or Username

It is possible to use both username and hostname restrictions at the same time. Normally Apache will require that both restrictions are satisfied, that is, that the user comes from an allowed host or domain name and that they supply a valid username and password. However the Satisfy any directive can be used in the .htaccess file or <Directory>, <Location> or <Files>, section. When this directive is given, anyone coming from the allowed domains will be given access without having to enter a username and password. All other users (from the "denied" domains) will be prompted for a username and password.

Quelle: Apache week

UPDATE: Auch interessant: http://www.javascriptkit.com/howto/htaccess.shtml

Apache Zugriff htaccess host ip-based password