[jQuery] Position a hidden DIV under a menu item

[[EMAIL PROTECTED]]

Hello,

I have an existing single-row table driven menu bar that I am looking
to add a drop-down menu to. Below is the code I am trying to use. I
have gone through many iterations but I seem to always get the same
error:

"$('#appMenuDropDown').style has no properties"

Can someone please take a look and offer a suggestion or two?
Thanks!
Derek

$(document).ready(function () {

        //hide the drop down menu DIV:
        $('#appMenuDropDown').hide();

        //Get the offset for the main menu bar item:
        var MainMenu = $('a#menuItem');
        var offset = MainMenu.offset();

        //Set the position of the hidden DIV:
        $('#appMenuDropDown').style.top = offset.top + 20 + 'px';
        $('#appMenuDropDown').style.left = offset.left + 'px';

        //Toggle showing the drop-down DIV:
        $('a#menuItem').mouseover(function() {
        $('#appMenuDropDown').toggle(400);
        return false;
        });
});