function move( id, spd )
{
	var obj=document.getElementById(id),max=-obj.offsetHeight+obj.parentNode.offsetHeight,top=parseInt(obj.style.top);
	if ((spd>0&&top<=0)||(spd<0&&top>=max))
	{
		obj.style.top=top+spd+"px";
		move.to=setTimeout(function(){ move(id,spd); },20);
	} else {
		obj.style.top=(spd>0?0:max)+"px";
	}
}