GRacias, he encontrado uno casi igual a lo que busco en esa web, es el siguiente...
Código: Seleccionar todo
############################################################## 
## MOD Title: Quick Reply with Quote 
## MOD Author: Smartor < smartor_xp@hotmail.com > (Hoang Ngoc Tu) http://smartor.is-root.com 
## MOD Description: This will add a quick-reply form below every topics 
##         It will only display when user has the Reply access 
##         User have a option to quote the last message 
## MOD Version: 1.1.3 
## 
## Installation Level: easy 
## Installation Time: 5 Minutes 
## Files To Edit: 3 
##   viewtopic.php 
##   language/lang_XX/lang_main.php 
##   templates/template_XX/viewtopic_body.tpl 
## Included Files: N/A 
############################################################## 
## Author Notes: 
## 
############################################################## 
## This MOD is released under the GPL License. 
## Intellectual Property is retained by the MOD Author(s) listed above 
############################################################## 
## Before Adding This MOD To Your Forum, You Should Back Up All Files Related To This MOD 
############################################################## 
# 
#-----[ OPEN ]------------------------------------------ 
# 
viewtopic.php 
# 
#-----[ FIND ]------------------------------------------ 
# 
$template->pparse('body'); 
include($phpbb_root_path . 'includes/page_tail.'.$phpEx); 
# 
#-----[ BEFORE, ADD ]------------------------------------ 
# 
// 
// Quick Reply Mod 
// 
if ( ((!$is_auth['auth_reply']) or ($forum_topic_data['forum_status'] == FORUM_LOCKED) or ($forum_topic_data['topic_status'] == TOPIC_LOCKED)) and ($userdata['user_level'] != ADMIN) ) 
{ 
   $quick_reply_form = ""; 
} 
else 
{ 
   if ( $can_watch_topic && $is_watching_topic ) 
   { 
      $notify = 1; 
   } 
   else 
   { 
      $notify = $userdata['user_notify']; 
   } 
   $bbcode_uid = $postrow[$total_posts - 1]['bbcode_uid']; 
   $last_poster = $postrow[$total_posts - 1]['username']; 
   $last_msg = $postrow[$total_posts - 1]['post_text']; 
   $last_msg = str_replace(":1:$bbcode_uid", "", $last_msg); 
   $last_msg = str_replace(":u:$bbcode_uid", "", $last_msg); 
   $last_msg = str_replace(":o:$bbcode_uid", "", $last_msg); 
   $last_msg = str_replace(":$bbcode_uid", "", $last_msg); 
   $last_msg = str_replace("'", "'", $last_msg); 
   $last_msg = "[QUOTE=\"$last_poster\"]" . $last_msg . "[/QUOTE]"; 
   $quick_reply_form = " 
   <script language='JavaScript' type='text/javascript'> 
      function checkForm() { 
         formErrors = false; 
         document.post.message.value = ''; 
         if (document.post.input.value.length < 2) { 
            formErrors = '" . $lang['Empty_message'] . "'; 
         } 
         if (formErrors) { 
            alert(formErrors); 
            return false; 
         } else { 
            if (document.post.quick_quote.checked) { 
               document.post.message.value = document.post.last_msg.value; 
            } 
            document.post.message.value += document.post.input.value; 
            return true; 
         } 
      } 
   </script> 
   <form action='".append_sid("posting.$phpEx")."' method='post' name='post' onsubmit='return checkForm(this)'> 
   <span class='genmed'><b>".$lang["Quick_Reply"].":</b><br />"; 
   if (!$userdata['session_logged_in']) 
   { 
      $quick_reply_form .= $lang['Username'] . ":&<input class='post' type='text' name='username' size='25' maxlength='25' value='' /><br />"; 
   } 
   $quick_reply_form .= "<textarea name='input' rows='10' cols='50' wrap='virtual' class='post''></textarea><br /> 
   <input type='checkbox' name='quick_quote' />".$lang["Quick_quote"]."<br /> 
   <input type='checkbox' name='attach_sig' checked='checked' />".$lang["Attach_signature"]."<br /> 
   <input type='hidden' name='mode' value='reply' /> 
   <input type='hidden' name='sid' value='" . $userdata['session_id'] . "' /> 
   <input type='hidden' name='t' value='" . $topic_id . "' /> 
   <input type='hidden' name='message' value='' /> 
   <input type='hidden' name='notify' value=" . $notify  . " /> 
   <input type='hidden' name='last_msg' value='" . $last_msg  . "' /> 
   <input type='submit' name='preview' class='liteoption' value='".$lang['Preview']."' />& 
   <input type='submit' name='post' class='mainoption' value='".$lang["Submit"]."' /> 
   </form></span>"; 
} 
$template->assign_vars(array( 
   'QUICK_REPLY_FORM' => $quick_reply_form) 
); 
// 
// END Quick Reply Mod 
// 
# 
#-----[ OPEN ]------------------------------------------ 
# 
language/lang_english/lang_main.php 
# 
#-----[ FIND ]------------------------------------------ 
# 
// That's all, Folks! 
# 
#-----[ BEFORE, ADD ]------------------------------------ 
# 
// Quick Reply Mod 
$lang['Quick_Reply'] = 'Quick Reply'; 
$lang['Quick_quote'] = 'Quote the last message'; 
# 
#-----[ OPEN ]------------------------------------------ 
# 
templates/subSilver/viewtopic_body.tpl 
# 
#-----[ FIND ]------------------------------------------ 
# 
{S_TOPIC_ADMIN} 
# 
#-----[ AFTER, ADD ]------------------------------------ 
# 
{QUICK_REPLY_FORM} 
# 
#-----[ SAVE/CLOSE ALL FILES ]------------------------------------------ 
# 
# EoM
total que el resultado es este, pero me surge una duda que debo hacer para centrar el cuadro de texto y ponerlo justo debajo del ultimo reply de la pagina ..

By 
bolinga