Vol"jin, Я знаю, что проще. Автор просил именно на JS.

<style>
DIV.clTop{position:absolute; width:170}
DIV.clSub{position:absolute; left:10; width:170}
#divCont{position:relative; left:100; top:0; height:400; width:170;}
A.clMain{font-family:Arial, Verdana, Helvetica, Helv; font-size:14px; text-decoration:none; font-weight:bold; color:black}
A.clSubb{font-family:Arial, Verdana, Helvetica, Helv; font-size:14px; text-decoration:none; color:black}
#divMain{position:absolute}
</style>
<script language="JavaScript">



var stayFolded=false


var n = (document.layers) ? 1:0;
var ie = (document.all) ? 1:0;
var browser=((n || ie) && parseInt(navigator.appVersion)>=4)


function makeMenu(obj,nest){
nest=(!nest) ? '':'document.'+nest+'.'
this.css=(n) ? eval(nest+'document.'+obj):eval('document.all.'+obj+'.style')
this.ref=(n) ? eval(nest+'document.'+obj+'.document'):eval('document');
this.height=n?this.ref.height:eval(obj+'.offsetHeight')
this.x=(n)? this.css.left:this.css.pixelLeft;this.y=(n)? this.css.top:this.css.pixelTop;
this.hideIt=b_hideIt; this.showIt=b_showIt; this.vis=b_vis; this.moveIt=b_moveIt
return this
}
function b_showIt(){this.css.visibility="visible"}
function b_hideIt(){this.css.visibility="hidden"}
function b_vis(){if(this.css.visibility=="hidden" || this.css.visibility=="hide" return true;}
function b_moveIt(x,y){this.x=x; this.y=y; this.css.left=this.x; this.css.top=this.y}

function init(){
oTop=new Array()
oTop[0]=new makeMenu('divTop1','divCont')
oTop[1]=new makeMenu('divTop2','divCont')
oTop[2]=new makeMenu('divTop3','divCont')
oTop[3]=new makeMenu('divTop4','divCont')
oTop[4]=new makeMenu('divTop5','divCont')
oTop[5]=new makeMenu('divTop6','divCont')
oSub=new Array()
oSub[0]=new makeMenu('divSub1','divCont.document.divTop1')
oSub[1]=new makeMenu('divSub2','divCont.document.divTop2')
oSub[2]=new makeMenu('divSub3','divCont.document.divTop3')
oSub[3]=new makeMenu('divSub4','divCont.document.divTop4')
oSub[4]=new makeMenu('divSub5','divCont.document.divTop5')
oSub[5]=new makeMenu('divSub6','divCont.document.divTop6')
for(i=0;i<oSub.length;i++){ oSub[i].hideIt() }
for(i=1;i<oTop.length;i++){ oTop[i].moveIt(0,oTop[i-1].y+oTop[i-1].height) }
}


function menu(num){
if(browser){
if(!stayFolded){
for(i=0;i<oSub.length;i++){
if(i!=num) oSub[i].hideIt()
}
for(i=1;i<oTop.length;i++){
oTop[i].moveIt(0,oTop[i-1].y+oTop[i-1].height)
}
}
oSub[num].vis()?oSub[num].showIt():oSub[num].hideIt()
for(i=1;i<oTop.length;i++){
if(!oSub[i-1].vis()) oTop[i].moveIt(0,oTop[i-1].y+oTop[i-1].height+oSub[i-1].height)
else oTop[i].moveIt(0,oTop[i-1].y+oTop[i-1].height)
}
}
}
if(browser) onload=init;
</script>




<div id="divCont">
<div id="divTop1" class="clTop"><a href="#" onclick="menu(0); return false" class="clMain">[choice 0]</a><br>
<div id="divSub1" class="clSub">
<a href="#" class="clSubb">-Sub 1</a><br>
<a href="#" class="clSubb">-Sub 2</a><br>
<a href="#" class="clSubb">-Sub 3</a><br>
<a href="#" class="clSubb">-Sub 4</a><br>
</div><br>
</div>
<div id="divTop2" class="clTop"><a href="#" onclick="menu(1); return false" class="clMain">[choice 1]</a><br>
<div id="divSub2" class="clSub">
<a href="#" class="clSubb">-Sub 1</a><br>
<a href="#" class="clSubb">-Sub 2</a><br>
</div><br>
</div>
<div id="divTop3" class="clTop"><a href="#" onclick="menu(2); return false" class="clMain">[choice 2]</a><br>
<div id="divSub3" class="clSub">
<a href="#" class="clSubb">-Sub 1</a><br>
<a href="#" class="clSubb">-Sub 2</a><br>
<a href="#" class="clSubb">-Sub 3</a><br>
</div><br>
</div>
<div id="divTop4" class="clTop"><a href="" onclick="menu(3); return false" class="clMain">[choice 3]</a><br>
<div id="divSub4" class="clSub">
<a href="#" class="clSubb">-Sub 1</a><br>
<a href="#" class="clSubb">-Sub 2</a><br>
</div><br>
</div>
<div id="divTop5" class="clTop"><a href="" onclick="menu(4); return false" class="clMain">[choice 4]</a><br>
<div id="divSub5" class="clSub">
<a href="#" class="clSubb">-Sub 1</a><br>
<a href="#" class="clSubb">-Sub 2</a><br>
<a href="#" class="clSubb">-Sub 3</a><br>
<a href="#" class="clSubb">-Sub 4</a><br>
<a href="#" class="clSubb">-Sub 5</a><br>
</div><br>
</div>
<div id="divTop6" class="clTop"><a href="" onclick="menu(5); return false" class="clMain">[choice 5]</a><br>
<div id="divSub6" class="clSub">
<a href="#" class="clSubb">-Sub 1</a><br>
</div><br>
</div>
</div>