the z-index on click..

the z-index on click..

hello evrybody, ...

i'm new with jquery and i wanted to create an effect but i can't understand where i'm making the mistake...
basically from a menu i'd like to pop-out the description of the element of the menu... in a "bubble"..
that should appear and disapper with a hover...

the problem is that underneath the menu there is  adiv with image, and the bubble go under it, even if i dynamically change the z-index.--- Doy uo know how this should work?.. this is the definition of css for the menu and and image and the script...

thanks a lot...

#menu li {
    display:block;
   float:left;
   list-style:none;
   margin:0;
   padding:0 10px 3px 0 ;
   right:40%;
   position:relative;  

}

#menu ul li a {
   display:block;
   margin:0 ;
   padding:0;
   background:#fff;
   font-family:"Georgia";
    font-size:16px;
    color:#4C4747;   
   text-decoration:none;  
   text-align:left;
}

#menu ul li a.active,
#menu ul li a.active:hover {
   color:#fff;
   background:#000;
   font-weight:bold;
}


#menu span
{
    background:url(images/ttbg2.jpg) no-repeat;
    width: 110px;
    height: 35px;
    position: absolute;
    font-family:"Georgia";
    font-size:10px;
    top: 10px;
    left: 0px;
    text-align: center;
    padding: 5px;
    display: none;
    line-height:110%;
    color:#000000;
    cursor:pointer;
}
#index_img{
   
    clear: left;   
    padding: 0;
    margin-left: 40%;   
    overflow:hidden;
    text-align:left;
    position:relative;
       
}

-----------------

jQuery(document).ready(function(){
    $("#menu li").hover(
        function(){
            $(this).find("span").attr({'z-index' : '100'})
            $(this).find("span").attr({
                "style": 'display:inline'
            });
            $(this).find("span").animate({opacity: 1, bottom: "+=10"}, {queue:false, duration:800});
        },
        function(){
            $(this).find("span").attr({'z-index' : '100'})
            $(this).find("span").animate({opacity: 0, top: "+=10"}, {queue:false, duration:800}, "linear",
                function(){
                    $(this).find("span").attr({"style": 'display:none'});           
                }
            );
        });
});