anche se è molto generica come domanda...

codice:
// add required fields and buttons
$content = preg_replace('/<input[^>]*type="submit"[^>]*>/', '
	<noscript>If you have enabled JavaScript, you will be able to preview your comment before submitting.
</noscript>
	<input type="hidden" name="author" id="actualauthor" value="" />
	<span id="submitbutton"><input name="submit" type="submit" id="submit" tabindex="6" value="Send comment" onclick="return dosubmit(0, sub_url);" /></span>
			
', $content);