function ShowLesson(Grade)
	{
	
	w= 600;
	h=400;
	l= (screen.AvailWidth - w) / 2;
	t= (screen.AvailHeight - h) / 2;

	popwin = window.open('Files/Flash/' + Grade + '.htm','Interactive_Tour','left=' + l + ', top=' + t + ', width=' + w + ', height=' + h);
	}