Upload the plugin directory moojax-comment-posting to the wp-content/plugins directory.
If you have already included the mootools framework in your template, edit the moojax-comment.php file to comment out duplicate inclusion of the library
Add the foillowing CSS classes to your template to style error messages and throbbers:
div.error {}
form.throbbing {}
For example, you can 'disable' the submit button during the submission with:
form.throbbing input[type="submit"]{display:none;}
Activate the plugin through the 'Plugins' menu in WordPress.