Upload the 'commentwitter' folder to the '/wp-content/plugins/' directory
Go into the WordPress admin interface and activate the plugin
3.(The following step is not needed if you are using the Thesis theme)
Insert the following PHP function where you would like the login prompt and text for the plugin:
<? getcommentwitterinput(); ?>
Note: This is usually right after:
<p><input name="submit" type="submit" id="submit" tabindex="5" value="Submit Comment" />