function login_win()
{
    var h=200;
    var w=300;
    window.open('login.php','','toolbar=no,menubar=no,location=no,status=no,scrollbars=no,resizable=no,height='+h+
',width='+w+',left='+(screen.availWidth-w)/2 + ',titlebar=no, top='+(screen.availHeight-h)/2 + '');
}