body {behavior: url(csshover.htc);}
div#menu {width: 100px;}
div#menu ul {padding: 0; width: 100px; border:1px solid; margin:0px;}
div#menu li.sousmenu {background: yellow;}
div#menu ul li {position:relative; list-style: none; border-bottom:1px solid;}
div#menu ul ul {position: absolute; top: 0; left: 100px; display:none}
div#menu li a {text-decoration: none;}
div#menu ul.niveau1 li.sousmenu:hover ul.niveau2, 
div#menu ul.niveau2 li.sousmenu:hover ul.niveau3 {display:block;}