#menu ul{
list-style: none; 
padding:0;
margin:0;
}
#menu li{
padding: 0; 
margin: 0;
float: left;
}
#menu a{
display: block;
width: 80px;
border-bottom: 1px dotted #555;
text-decoration: none;
color: #555;
padding: 0 0 0 20px;
margin: 0 2px;
font-size: x-small;
text-align: left;
}
#menu a:hover{
background:url(画像のアドレス) no-repeat left center;
}