You will need the ruby-ldap and highline libraries.
Ruby LDAP can be found at:
http://ruby-ldap.sourceforge.net/
Highline can be installed through rubygems:
$ gem install highline
Stick the config.yml in /etc/adduser-ldap, and edit it for your site.
Then, use ./adduser-ldap like you would any regular adduser program.
By default, it will bind as the user running it, so they should have
administrative privileges to the directory.