function getWindowHeight() {
  var myHeight = 0;
  if( typeof( window.innerHeight ) == 'number' ) {
    //Non-IE
    myHeight = window.innerHeight;
  } else if( document.documentElement && document.documentElement.clientHeight ) {
    //IE 6+ in 'standards compliant mode'
    myHeight = document.documentElement.clientHeight;
  } else if( document.body && document.body.clientHeight ) {
    //IE 4 compatible
    myHeight = document.body.clientHeight;
  }
  var top;
  compareHeight = document.getElementById('outerwrap').offsetHeight;
//  alert(compareHeight + ' en ' + myHeight);
  if (myHeight<compareHeight)
  {
	top = 0;
  } else {
	top = Math.round((myHeight-compareHeight)/2);
  }
  document.body.style.backgroundPosition = '0px ' + top.toString()+'px';
  document.getElementById('outerwrap').style.top=top.toString()+'px'
}