th.header { 
    background-image: url(bg.gif);     
    cursor: pointer; 
    font-weight: bold; 
    background-repeat: no-repeat; 
    background-position: center left; 
    padding-left: 16px; 
    margin-left: -1px; 
    padding-right: 16px; 
}
th.headerSortUp { 
    background-image: url(desc.gif);
}

th.headerSortDown { 
    background-image: url(asc.gif);
}