Replaces the built-in CAPTCHA on member registration and comment forms with sweet CAPTCHA.
Just go to http://www.sweetcaptcha.com/register.php, replace sweetcaptchalib/sweetcaptcha.php with the downloaded file, and place this directory under expressionengine/third-party.
You also need to make sure you replace the SWEETCAPTCHA_PUBLIC_URL value with the actual path to the downloaded sweetcaptcha.php, usually expressionengine/third_party/sweetcaptcha/sweetcaptchalib/sweetcaptcha.php.