codice:
include "config.inc.php";

class myclass
{
    function myclass()
    {
     $this->conn = mysql_connect($this->dbhost, $this->dbuser,$this->dbpass);
    mysql_select_db ($this->dbname);
    }
    .
    .
    .
    .
}

$db = new myclass();
$db->dbname = $config['sql_name'];//var presenti nel file config.inc.php
$db->dbuser = $config['sql_user'];
$db->dbpass = $config['sql_pass'];
$db->dbhost = $config['sql_host'];
Prova così...