$(window).load(function(){
    if (document.images) {
        var imgs = new Object();
        imgs[0] = new Image();
        imgs[0].src = "/images/green_but_hover.png";
        imgs[1] = new Image();
        imgs[1].src = "/images/but_orange_hover.png";
        imgs[2] = new Image();
        imgs[2].src = "/images/but_blue_hover.png";
        imgs[3] = new Image();
        imgs[3].src = "/images/but_pink_hover.png";
        imgs[4] = new Image();
        imgs[4].src = "/images/but_green2_hover.png";
        imgs[5] = new Image();
        imgs[5].src = "/images/but_orange2_hover.png";
    }
    $('#menu ul li a').each(function(index){
        $(this).mouseenter(function() { 
            $(this).css('background','url("'+imgs[index].src+'") center no-repeat');  
        });
        $(this).mouseout(function() { 
            $(this).css('background','');      
        });
    });  
});