function mostra(layer,pos,offx,offy)
{
  var obj = document.getElementById(pos);
  var left = 0;
  var top = 0;

  do
    {
      left += obj.offsetLeft;
      top += obj.offsetTop;
      obj = obj.offsetParent;
    }
  while (obj != null);

  var lay = document.getElementById(layer);
  lay.style.left = (left + offx) + "px"; 
  lay.style.top = (top + offy) + "px";
  lay.style.visibility = "visible";
}


function oculta(layer)
{
  document.getElementById(layer).style.visibility = "hidden";
}