I would say that it is easy, but it all depends on how familiar you are doing LDAP queries and with where to find authentication data in your LDAP server. In my experience, lack of LDAP knowledge causes the biggest problems for people trying to configure a server for authentication. If you have little LDAP experience, you should read up on the basics and get an LDAP client (such as the freeware version of Softerra's LDAP Browser:
http://www.ldapbrowser.com/) to explore your LDAP schema and try out queries.
Adding modules to Apache is easy. Your httpd.conf file has plenty of examples that you could copy, because of all the modules that are included by default. The Apache documentaion at
http://httpd.apache.org/docs/1.3/configuring.html#modules (and the links to documentation for the related directives) ought to tell you everything that you need to know.