I m supposing following code according to your description..

<div style="position: absolute; display: none;" id="menu">
   <!-- menu stuff in here -->
</div>
<div id="placeholder">Hover over me to show the menu here</div>

then you can use the following JavaScript code :

$("#placeholder").mouseover(showMenu);

var showMenu = function(ev) {
  //get the position of the placeholder element
  var pos = $("#placeholder").offset();  
  var width = $("#placeholder").width();
  //show the menu directly over the placeholder
  $("#menu").css( { "left": (pos.left + width) + "px", "top":pos.top + "px" } );
  $("#menu").show();
}