Redmine

I'm trying to install Redmine, but I am getting this error when I run Step 6
(RAILS_ENV=production rake db:migrate):

rake aborted!
Please install the postgresql adapter: `gem install activerecord-postgresql-adapter` (cannot load such file -- pg_ext)
/root/redmine-2.2/lib/plugins/acts_as_activity_provider/init.rb:2:in `block in <top (required)>'
/root/redmine-2.2/config/initializers/00-core_plugins.rb:12:in `eval'
/root/redmine-2.2/config/initializers/00-core_plugins.rb:12:in `block in <top (required)>'
/root/redmine-2.2/config/initializers/00-core_plugins.rb:2:in `each'
/root/redmine-2.2/config/initializers/00-core_plugins.rb:2:in `<top (required)>'
/root/redmine-2.2/config/environment.rb:14:in `<top (required)>'
Tasks: TOP => db:migrate => environment
(See full trace by running task with --trace)

My OS is Fedora 17

Thanks,

Andrew