Prototype.Browser.IE6 = Prototype.Browser.IE && parseInt(navigator.userAgent.substring(navigator.userAgent.indexOf("MSIE")+5)) == 6;
Prototype.Browser.IE7 = Prototype.Browser.IE && parseInt(navigator.userAgent.substring(navigator.userAgent.indexOf("MSIE")+5)) == 7;
Prototype.Browser.IE8 = Prototype.Browser.IE && !Prototype.Browser.IE6 && !Prototype.Browser.IE7;


function positionSirene()
{

  var windowHeight = document.viewport.getHeight();
  var element = $('sirene');
  
  if(Prototype.Browser.IE6)
  {
    return;
  }     
  
  if(windowHeight > 470)
	  element.setStyle({
	    position: 'fixed',
	    display: 'block',
	    marginTop: (windowHeight - 470) + 'px'
	  });
	else 
    element.setStyle({
      position: 'static',
      display: 'block',
      marginTop: '0px'
    });	
}

document.observe("dom:loaded", positionSirene);
new Event.observe(window, 'resize', positionSirene);