Models not loading?

I've followed all the installation instructions at
for an OS X install. Everything seems to work fine in that I can
create a rails project and run rake tasks, migrations, start a server
etc. But it seems that my models are not being loaded. For example,
when I try to access a model via the console, I get the following:

?> User.find(:all)
NameError: uninitialized constant User
        from /usr/local/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/
active_support/dependencies.rb:266:in `load_missing_constant'
        from /usr/local/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/
active_support/dependencies.rb:452:in `const_missing'
        from /usr/local/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/
active_support/dependencies.rb:464:in `const_missing'
        from (irb):2

Needless to say, running the server and trying to go to users/index or
any other action gives me a routing error. For what it's worth I'm
on: Rails 1.2.3, Ruby 1.2.6, Mac OS X 10.4.10, Mongrel 1.0.1

I've been working with RoR for a few months on windows machines and
have not run into this issue even after several different
installations. However, I've been working with Windows for many years
and with Mac only for a few days so it is very possible that I have
missed something obvious here.

You've confirmed that the database.yml file is set up correctly?