simple captcha instllation problems on rails 3.0.7

I have installed SimpleCaptcha plugin to vendor/plugin

For the setup the plugin I am getting

rake simple_captcha:setup

Gives me error: rake aborted! Don't know how to build task 'simple_captcha:setup'

I checked rails version by

gem list

rails (3.0.7) railties (3.0.7) rake (0.9.0, 0.8.7) rake-compiler (0.7.8) rmagick (2.13.1) rubygems-update (1.8.3)

ruby -v

ruby 1.9.2p180 (2011-02-18 revision 30909) [i686-linux]

I am looking for help on this.