How to use the template functions to add link to Twitter?

I think I am on a good way:

<div class="the_comment">
<p><?php comment_author_link(); ?>
<a rel="nofollow" href="<?php comment_author_twitter_url($comment_id); ?>">
(Twitter: <?php comment_author_twitter_id($comment_id); ?>)
</a><br />
<span class="small-text"><a href="comment-<?php comment_ID(); ?>"><?php comment_date('F d, Y'); ?></a></span></p>
<?php comment_text(); ?>
</div>

How should I modify this code to make the Twitter link appear only when there is an entry in the database (and only when the plugin is activated – otherwise the comments would not appear at all when the plugin is not active).

And is there any way to include this field in anti-spam filtering in case a spammer writes the comment here?

Anyone?

OK, I got it (by trial and error more or less). It appears to be working fine. In case someone finds it useful, here it is:

<?php
if (function_exists('get_comment_author_twitter_id')) {
	$twittername = get_comment_author_twitter_id($comment_id);
		if ( $twittername ) {
			echo '<a rel="nofollow" href="';
			comment_author_twitter_url($comment_id);
			echo '">(';
			comment_author_twitter_id($comment_id);
			echo ')</a>';
		}
}
?>

Nice to know that you figured it out.