Comment form introduction text

you theme might have a comments.php; edit this;

look for comment_form()

http://codex.wordpress.org/Function_Reference/comment_form

one possibility:
for instance, try to use the following:

<?php comment_form(array('comment_notes_before' => '<p class="comment-notes">' . __( 'Your email address will not be published.' ) . ( $req ? $required_text : '' ) . '<br/>YOUR INTRO TEXT HERE</p>')); ?>

other possibility:

add your intro text before the line with ‘comment_form();’

you could paste the code of comments.php into a http://wordpress.pastebin.com/ and post the link to it here.
someone might have a look at it and might have some suggestions.