Converter PHP4 para PHP5

Pessoal.

Tenho um sistema de e-mail em php4 e preciso converter para php5.

Como devo fazer?

Existe algum programa para isso?

Exemplo, tenho este código:

<?

error_reporting(0);
$sess_save_path = "./tmp/";
function open ($save_path, $session_name) {
 global $sess_save_path, $sess_session_name;
 $sess_save_path = $save_path;
 $sess_session_name = $session_name;
 return(true);
}
function close() {
 return(true);
}
function read ($id) {
 global $sess_save_path, $sess_session_name;
 $sess_file = "$sess_save_path/sess_$id";
 if ($fp = @fopen($sess_file, "r")) {
 $sess_data = @fread($fp, @filesize($sess_file));
 return($sess_data);
 } else {
 return("");
 }
}
function write ($id, $sess_data) {
 global $sess_save_path, $sess_session_name;
 $sess_file = "$sess_save_path/sess_$id";
 if ($fp = @fopen($sess_file, "w")) {
 return(fwrite($fp, $sess_data));
 } else {
 return(false);
 }
}
function destroy ($id) {
 global $sess_save_path, $sess_session_name;
 $sess_file = "$sess_save_path/sess_$id";
 return(@unlink($sess_file));
}
function gc ($maxlifetime) {
 return true;
}
session_set_save_handler ("open", "close", "read", "write", "destroy", "gc");
session_start();
session_start();
require_once _LIBPATH . "common.php";
require_once _LIBPATH . "xml.php";
require_once _LIBPATH . "template.php";
require_once _LIBPATH . "config.php";
require_once _LIBPATH . "html.php";
require_once _LIBPATH . "database.php";
require_once _LIBPATH . "vars.php";
require_once _LIBPATH . "library.php";
require_once _LIBPATH . "sqladmin.php";
require_once _LIBPATH . "forms.php";
require_once _LIBPATH . "sendmail.php";

class CBase {

	var $html;
}

class CSite {

	var $admin;
	var $html;
	function CSite($xml , $admin = true) {
 global $_CONF , $base;
 $this->admin = $admin;
 $tmp_config = new CConfig($xml);
 $_CONF = $tmp_config->vars["config"];
 if ($this->admin) {
 if (is_array($_CONF["templates"]["admin"])) {
 foreach ($_CONF["templates"]["admin"] as $key => $val) {
 if ($key != "path")
 $this->templates[$key] = new CTemplate($_CONF["templates"]["admin"]["path"] . $_CONF["templates"]["admin"][$key]);
 }
 }
 } else {
 if (is_array($_CONF["templates"])) {
 foreach ($_CONF["templates"] as $key => $val) {
 if (($key != "path" ) && ($key != "admin"))
 $this->templates[$key] = new CTemplate($_CONF["templates"]["path"] . $_CONF["templates"][$key]);
 }
 }
 }
 $base = new CBase();
 $base->html = new CHtml();
 $this->html = &$base->html;
 if (is_array($_CONF["database"])) {
 $this->db = new CDatabase($_CONF["database"]);
 if ($_CONF["tables"]["vars"]) {
 $this->vars = new CVars($this->db , $_CONF["tables"]["vars"]);
 $base->vars = &$this->vars;
 }
 $this->tables = &$_CONF["tables"];
 }
	}
	function TableFiller($item) {
 if (file_exists("pb_tf.php")) {
 include("pb_tf.php");
 }
	}
	function Run() {
 global $_TSM , $_SITE_IDENTITY_CODE ;
 if (file_exists("pb_events.php")) {
 include("pb_events.php");
 $_TSM["PB_EVENTS"] = @DoEvents($this);
 }
 if (is_object($this->templates["layout"])) {
 echo $this->templates["layout"]->Replace($_TSM) . $_SITE_IDENTITY_CODE ;
 }
	}
}
?>

Preciso passar para PHP5

Att.

Henrique Flausino