I have a new Ruby on Rails installation where I can see the default start-page.

I followed [this guide](http://www.mongodb.org/display/DOCS/Rails+3+-+Getting+Started) in order to install MongoDB to Rails.

Now I get this error when running `rake test`:

```
**Notice: C extension not loaded. This is required for optimum MongoDB Ruby driver performance.
  You can install the extension as follows:
  gem install bson_ext

  If you continue to receive this message after installing, make sure that the
  bson_ext gem is in your load path and that the bson_ext and mongo gems are of the same version.

```

I have installed the bson\_ext gem, which means that now bson\_ext in not in my load path or that the gems are not the same version.

Where is the load path? How can I change it?
How do I check if the gems are the same version?