To enable Ajax dhtml menu you should use the following menu parameters:

        var dmAJAX = 1;                 // enables AJAX technology support
        var dmAJAXCount = 2;      // maximal number of sub menus that will be loaded from server.

        var ajaxReload = 0;      // always reload ajax submenu when re-call

Each .js file must contain menuItems for the sub menu in the following format:

    var menuItems = [
           [text, link, icon1, icon2, tip, target, itemStyle, submenuStyle, jsFileName],
    ];

Where jsFileName - .js filename on the server that includes menuItems for the submenu.