simple captcha instllation problems

I am running XP. Downloaded simple captcha from expressica, unzipped into
vendor/plugin. Ran

rake simple_captcha:setup.

Gives me error: rake aborted! don't know how to build task 'simple
I checked rails version by

gem list rails

Gives me rails <2.3.5, 1,2,2>
can someone tell me how to fix this?