function fundo()
{
  if (screen.width == 800 && screen.height == 600)
  {
    document.body.background='fundo1.jpg';
  }
  if (screen.width == 1024 && screen.height == 768)
  {
    document.body.background='fundo.JPG'; 
  }	
}  
function janela()
{
  window.open("comentario.php","Comentarios", "width=500, height=500, status=no, location=no, menubar=no, toolbar=no, scrollbars=yes");
}