function opacity(id, millisec) {
	//speed for each frame
	var speed = Math.round(millisec / 100);
	var timer = 0;
  var obj = document.getElementById(id); 
  
  if(obj.className=='active'){
		for(i = 100; i >= 0; i--) {
			setTimeout("changeOpac(" + i + ",'" + id + "')",(timer * speed));
			timer++;
		}
		obj.className='unactive';
    obj.style.display="none";
  } else {
    obj.style.display="block";
		for(i = 0; i <= 100; i++)
			{
			setTimeout("changeOpac(" + i + ",'" + id + "')",(timer * speed));
			timer++;
		}
    obj.className='active';  
  }
}

//change the opacity for different browsers
function changeOpac(opacity, id) {
	var object = document.getElementById(id).style; 
	object.opacity = (opacity / 100);
	object.MozOpacity = (opacity / 100);
	object.KhtmlOpacity = (opacity / 100);
	object.filter = "alpha(opacity=" + opacity + ")";
}