betternestedset outside of rails

Hi

I've been putting together database scripts that rely on Active Record
outside of rails - this link was very helpful in getting started:
http://ollehost.dk/blog/?p=214

Now though, I'm having a problem getting this to work with
betternestedset.

Can anyone tell me how to require these nested methods in an external
script? These don't seem to pick them up:

require 'rubygems'
require 'active_record'

My error is:

C:/MyDevelopment/InstantRails/ruby/lib/ruby/gems/1.8/gems/
activerecord-1.15.3/lib/active_record/base.rb:1860:in
`method_missing': undefined method `move_to_child_of' for
#<Employeetree:0x9466a28> (NoMethodError)

thanks!
Andrew