rspec upgrade from 1.2.6 to 2.0.2 and/or 2.1.0

I am trying to upgrade a Rails 1.2.6 application to either 2.0.2 or
(preferably) 2.1.0 whichever works. The application has a hugh number
of rspec tests written. I am having problems getting past the first
Details: The application has both rspec (1.1.3) and rspec_on_rails
plugins installed in vendor/plugins directory. The application also had
Rails 1.2.6 frozen in the vendor directory. When I ran the following
code snippet in the account_spec.rb file, it ran fine (with Rails 1.2.6
frozen in vendor directory).

require File.dirname(__FILE__) + '/../spec_helper'

describe Account do
  it "should have valid fixture defaults" do
    create_account.should be_valid

"create_account" exists in the spec_helper.rb.

Now to upgrade, first in Rails 2.0.2. I removed the Rails directory
from vendor directory, changed rails version in environment.rb from
1.2.6 to 2.0.2 and tried to rerun the same file/test as above. The code
does not even get past the first line of code, i.e., require
File.dirname ....

I get the following exception trace:

`load_missing_constant': Expected
/home/bruparel/work/isabont/app/models/employer.rb to define Employer

I am no rspec power user at this point, but have run rspec tests at
commmand line and in NetBeans IDE for Rails 1.2.x without any problems.
Thanks for your time.

         ... 15 levels...
        from /home/bruparel/work/isabont/vendor/plugins/rspec/bin/spec:4

The immediate problem has been solved with the help of someone who is
familiar with it.
The app used acts_as_list and acts_as_tree which was getting lost in the
stack trace. Since Rails 2.x has removed that from core, I had to
install them as plug-ins. It is working on Rails 2.0.2, next I will
attempt 2.1