Простой пример:
<html>
<head>
<title>Test</title>
<style type="text/css">
.mn {
border-bottom:#B6BCC6 1px solid;
border-top:#B6BCC6 1px solid;
}
.sm {
visibility:hidden;
position:absolute;
border-left:2px #B6BCC6 solid;
border-right:2px #B6BCC6 solid;
border-bottom:2px #B6BCC6 solid;
background-color:#F5F5F5;
}
</style>
<script type="text/javascript">
var oldId;
function omo(ml,m){ ex(ml); oldId = ml; }
function hi(elem) { document.getElementById(elem).style.visibility = 'hidden'; }
function ex(elem) { document.getElementById(elem).style.visibility = 'visible'; }
</script>
</head>
<body bgcolor="#E8EAEF">
<table width='750' cellpadding='0' cellspacing='0' border='0' align='center'>
<tr>
<td class='mn' width='20'></td><td class='mn' id='m1' onMouseOver="omo('ml1','m1')" onMouseOut="hi('ml1')"><a href='/video' class='menu' onClick='return false;'>Video</a></td>
<td class='mn' width='20'></td><td class='mn' id='m2' onMouseOver="omo('ml2','m2')" onMouseOut="hi('ml2')"><a href='/foto' class='menu' onClick='return false;'>Foto</a></td>
<td class='mn' width='20'></td><td class='mn' id='m3' onMouseOver="omo('ml3','m3')" onMouseOut="hi('ml3')"><a href='/music' class='menu' onClick='return false;'>Music</a></td>
</tr>
<tr>
<td></td><td><div id='ml1' onMouseOver="ex('ml1')" onMouseOut="hi('ml1')" class='sm'>
<nobr>
<a href='#'>dasasdasas</a><br>
<a href='#'>dasdasdasdasdasdas</a><br>
<a href='#'>dsadasdadsadsadasdas</a><br>
<a href='#'>dsadsasadasdasdasas</a><br>
<a href='#'>dsaaddasdasasdasds</a><br>
</nobr>
</div></td>
<td></td><td><div id='ml2' onMouseOver="ex('ml2')" onMouseOut="hi('ml2')" class='sm'>
<nobr>
<a href='#'>dasasdasas</a><br>
<a href='#'>dasdasdasdasdasdas</a><br>
<a href='#'>dsadasdadsadsadasdas</a><br>
<a href='#'>dsadsasadasdasdasas</a><br>
<a href='#'>dsaaddasdasasdasds</a><br>
</nobr>
</div></td>
<td></td><td><div id='ml3' onMouseOver="ex('ml3')" onMouseOut="hi('ml3')" class='sm'>
<nobr>
<a href='#'>dasasdasas</a><br>
<a href='#'>dasdasdasdasdasdas</a><br>
<a href='#'>dsadasdadsadsadasdas</a><br>
<a href='#'>dsadsasadasdasdasas</a><br>
<a href='#'>dsaaddasdasasdasds</a><br>
</nobr>
</div></td>
</tr>
</table>
</body>
</html>
Примерно как-то так.
А вообще можешь поразбирать код на сайтах, где есть меню, если что-то не поймешь...