(function($) {
	$.extend($.fx.step,{
	    backgroundPosition: function(fx) {
            if (fx.state === 0 && typeof fx.end == 'string') {
                var start = $.curCSS(fx.elem,'backgroundPosition');
                start = toArray(start);
                fx.start = [start[0],start[2]];
                var end = toArray(fx.end);
                fx.end = [end[0],end[2]];
                fx.unit = [end[1],end[3]];
			}
            var nowPosX = [];
            nowPosX[0] = ((fx.end[0] - fx.start[0]) * fx.pos) + fx.start[0] + fx.unit[0];
            nowPosX[1] = ((fx.end[1] - fx.start[1]) * fx.pos) + fx.start[1] + fx.unit[1];
            fx.elem.style.backgroundPosition = nowPosX[0]+' '+nowPosX[1];

           function toArray(strg){
               strg = strg.replace(/left|top/g,'0px');
               strg = strg.replace(/right|bottom/g,'100%');
               strg = strg.replace(/([0-9\.]+)(\s|\)|$)/g,"$1px$2");
               var res = strg.match(/(-?[0-9\.]+)(px|\%|em|pt)\s(-?[0-9\.]+)(px|\%|em|pt)/);
               return [parseFloat(res[1],10),res[2],parseFloat(res[3],10),res[4]];
           }
        }
	});
})(jQuery);

  $(function(){
    	$('#a a.a')
    		.css( {backgroundPosition: "0 0"} )
    		.mouseover(function(){
    			$(this).stop().animate({backgroundPosition:"(0px 38px)"}, {duration:100})
    		})
    		.mouseout(function(){
    			$(this).stop().animate({backgroundPosition:"(0px 0px)"}, {duration:500, complete:function(){
    				$(this).css({backgroundPosition: "0px 0px"})
    			}})
    		})
    	$('#a a.b')
    		.css( {backgroundPosition: "-240px 0"} )
    		.mouseover(function(){
    			$(this).stop().animate({backgroundPosition:"(-240px 38px)"}, {duration:100})
    		})
    		.mouseout(function(){
    			$(this).stop().animate({backgroundPosition:"(-240px 0px)"}, {duration:500, complete:function(){
    				$(this).css({backgroundPosition: "-240px 0px"})
    			}})
    		})
    	$('#a a.c')
    		.css( {backgroundPosition: "-480px 0"} )
    		.mouseover(function(){
    			$(this).stop().animate({backgroundPosition:"(-480px 38px)"}, {duration:100})
    		})
    		.mouseout(function(){
    			$(this).stop().animate({backgroundPosition:"(-480px 0px)"}, {duration:500, complete:function(){
    				$(this).css({backgroundPosition: "-480px 0px"})
    			}})
    		})
    	$('#a a.d')
    		.css( {backgroundPosition: "-720px 0"} )
    		.mouseover(function(){
    			$(this).stop().animate({backgroundPosition:"(-720px 38px)"}, {duration:100})
    		})
    		.mouseout(function(){
    			$(this).stop().animate({backgroundPosition:"(-720px 0px)"}, {duration:500, complete:function(){
    				$(this).css({backgroundPosition: "-720px 0px"})
    			}})
    		})
    });