Using a gem as the model Rails 3/datamapper

I have a non-rails ruby application that has many models that we now
need to create a rails application for. These models are managed as a
gem. How can that gem be used in a rails3 app? How do you specify that
gem and put it somewhere where the rails can find it? Was making the
model library a gem the right thing to do. It has worked well for us
so far.

Don F.

can anyone help on this?