function openWindow(pagina,target,width,height)
{
  var newWidth;
  var newHeight;
  var win;
  if ((width == 0) && (height == 0))
    win = window.open(pagina,target);	
  else
  {
    newWidth = (screen.availWidth-10 - width) / 2;
    newHeight = (screen.availHeight-20 - height) / 2;    
    win = window.open(pagina,target,"width="+width+",height="+height+",location=no,scrollbars=yes,menubars=no,directores=no,copyhistory=no,toolbars=no,resizable=no,left=" + newWidth + ",top=" + newHeight);
    win.moveTo(newWidth, newHeight);
    win.focus();
  }
  return(true);
}