<script language="JavaScript" type="text/JavaScript">
<!--
function MM_findObj(n, d) { //v4.01
  var p,i,x;  if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
    d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
  if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
  for(i=0;!x&&d.layers&&i<d.layers.length;i++) x=MM_findObj(n,d.layers[i].document);
  if(!x && d.getElementById) x=d.getElementById(n); return x;
}

function MM_showHideLayers() { //v6.0
  var i,p,v,obj,args=MM_showHideLayers.arguments;
  for (i=0; i<(args.length-2); i+=3) if ((obj=MM_findObj(args[i]))!=null) { v=args[i+2];
    if (obj.style) { obj=obj.style; v=(v=='show')?'visible':(v=='hide')?'hidden':v; }
    obj.visibility=v; }
}
//-->
</script>

<style>
/*스타일 시트에서 추가해줄부분*/
.top_menu_btn a {
text-decoration: none;
position: relative;
display: block;
margin-top: 3px;
}

.top_menu_btn a:hover {
text-decoration: none;
margin-top: 5px;
}
</style>

<!-- layer menu -->
<table width='400' border="1" cellpadding="0" cellspacing="2" border="0" class="top_menu_btn">
<tr>
<td valign="top"><a href="" onMouseOver="MM_showHideLayers('TopMenu1','','show','TopMenu2','','hide')" onfocus='this.blur()'>메뉴1</a></td>
<td valign="top"><a href="" onMouseOver="MM_showHideLayers('TopMenu1','','hide','TopMenu2','','show')" onfocus='this.blur()'>메뉴2</a></td>
<td background="" valign="top"><a href="" onMouseOver="MM_showHideLayers('TopMenu1','','hide','TopMenu2','','hide')" onfocus='this.blur()'>메뉴3</a></td>
<td background="" valign="top"><a href="" onMouseOver="MM_showHideLayers('TopMenu1','','hide','TopMenu2','','hide')" onfocus='this.blur()'>메뉴4</a></td>
</tr>
</table>
<!-- /layer menu -->

*참고로 아래 서브메뉴 부분은 테이블태그에 구애받지 마시고 <body>태그 바로아래 두는 것이 위치제어를 위해 좋습니다.

<!-- layer menu sub 위치제어를 위해 내어옮김 -->
<div id="TopMenu1" style="position:absolute; width:780px; height:30px; z-index:1; left: 300px; top: 450px; visibility: hidden;">
<table width='300' cellpadding="0" cellspacing="0" border='1' class="top_menu_btn">
<tr>
<td><a href="l" title="">서브1</a></td>
<td><a href="" title="">서브2</a></td>
<td><a href="" title="">서브3</a></td>
<td><a href="" title="">서브4</a></td>
</tr>
</table>
</div>
<div id="TopMenu2" style="position:absolute; width:780px; height:30px; z-index:1; left: 400px; top: 450px; visibility: hidden;">
<table width='300' cellpadding="0" cellspacing="0" border='1' class="top_menu_btn">
<tr>
<td><a href="" title="">서브a</a></td>
<td><a href="" title="">서브b</a></td>
<td><a href="" title="">서브c</a></td>
<td><a href="" title="">서브d</a></td>
</tr>
</table>
</div>