How to install acts_as_threaded

Hi,everyone
I'm a freshman for study ROR,I was try to deal the book<Beginnig Ruby
on rails E-Commerce>.
When I was in chap 6,it need to install a plugin that call
acts_as_threaded.But I can't deal with it.
I had used gem install and ruby script/plugin install.If you know how
to deal with it ,please give me a favor!

I doubt you're going to have much luck getting that plugin installed
on a modern Rails stack; it's old enough that it depended on the built-
in acts_as_nested_set stuff which was split off into a plugin back in
2007(?).

The book's code examples run on Rails 1.1.6; I'd recommend that you
find a book that at least deals with Rails 2, as getting code examples
from 2006 running today will be seriously difficult for a new
developer.

--Matt Jones

Thanks a lot ! I use this book ,beacuse I want to study in a difficult model.I think it was good for my plan to learn ROR.