var speed = 50;        
var max_opacity = 100;  
var min_opacity = 10;	
var do_step  =  5;      

	function change_opacity(obj,do_option)
	{
		if(obj.doing)
			clearInterval(obj.doing);
		obj.doing = setInterval(do_option+"_alpha("+obj.sourceIndex+")",speed);	
	}
	

	function down_alpha(obj_index)
	{
		var obj = document.all[obj_index];
		
		if(obj.filters.Alpha.Opacity > min_opacity )
		{
			obj.filters.Alpha.Opacity += -do_step;
		}	
		else
		{	
			clearInterval(obj.doing);
			obj.filters.Alpha.Opacity = min_opacity;
			obj.doing = false;
		}	
	}	
	function up_alpha(obj_index)
	{
		var obj = document.all[obj_index];
		
		if(obj.filters.Alpha.Opacity<max_opacity)
			obj.filters.Alpha.Opacity += do_step;
		else
		{	
			clearInterval(obj.doing);
			obj.filters.Alpha.Opacity = max_opacity;
			obj.doing = false;
		}	
	}