The scenario - CentOS 4.3 with standard Apache setup. Do a 'yum install httpd' to install Apache and a 'yum install mod_authz_ldap' to install the LDAP authentication module we'll be using.
For any other platforms, it shouldn't be much different.
The next thing we need to do is setup some things on AD. Active Directory works on the basis that you need to bind to it to authenticate. OpenLDAP allows anonymous binded users to authenticate ... unfortunately Active Directory does not AFAIK (at least this is what it took to get it to work for me)
Logon to the AD server and: