Javascript menu

Hi,
I believe this is a simple fix, but since I am not savvy in javascript, it is not for me.
I have a drop down menu with 3 main sections, when clicked each section expands to multiple buttons. My end goal is to have the submenu stay expanded when in that section. So when you click NILS it will expand and stay expanded even when you click on a NILS sub menu and go to that page. It will only collapse when you click on Forms or AuthenticWeb.
I appreciate the help. Thanks.

<script type="text/javascript">
<!--
window.onload=montre;
function montre(id) {
var d = document.getElementById(id);
    for (var i = 1; i<=10; i++) {
        if (document.getElementById('smenu'+i)) {document.getElementById('smenu'+i).style.display='none';}
    }
if (d) {d.style.display='block';}
}
//-->
</script>
<div>
                                        <dl id="menu">
                                            <dt>PRODUCTS</dt>
                                            <dt onclick="javascript:montre('smenu2');">[+]<font color="#78b7d9">__</font>NILS</dt>
                                            <dd id="smenu2">
                <ul>
                    <li><a href="nils.html">Overview</a></li>
                    <li><a href="nils_prod/nils_insource.html">NILS INsource</a></li>
                    <li><a href="nils_prod/nils_incompass.html">NILS INcompass</a></li>
                    <li><a href="nils_prod/nils_mce.html">Market Conduct Exam Tools</a></li>
                    <li><a href="nils_prod/nils_complianceware.html">ComplianceWare</a></li>
                    <li><a href="nils_prod/nils_redbooks.html">NILS Red Books</a></li>
                </ul>
            </dd>    

        <dt onclick="javascript:montre('smenu3');">[+]<font color="#78b7d9">__</font>AuthenticWeb</dt>
            <dd id="smenu3">
                <ul>
                    <li><a href="authenticweb.html">Overview</a></li>
                    <li><a href="authenticweb/authenticweb_cancellation.html">Cancellation & Nonrenewal</a></li>
                    <li><a href="authenticweb/authenticweb_claims.html">Claims</a></li>
                    <li><a href="authenticweb/authenticweb_contract.html">Contract Provisions</a></li>
                    <li><a href="authenticweb/authenticweb_statefiling.html">State Filing</a></li>
                    <li><a href="authenticweb/authenticweb_um_uim.html">UM/UIM Coverage Rejection</a></li>
                    <li><a href="authenticweb/authenticweb_matrices.html">AuthenticWeb Matrices</a></li>
                </ul>
            </dd>

        <dt onclick="javascript:montre('smenu4');">[+]<font color="#78b7d9">__</font>Forms</dt>
            <dd id="smenu4">
                <ul>
                    <li><a href="forms.html">Overview</a></li>
                    <li><a href="forms/preprinted_forms.html">Preprinted</a></li>
                    <li><a href="forms/electronic_forms.html">Electronic</a></li>
                    <li><a href="forms/integration_services.html">Intregration Services</a></li>
                    <li><a href="forms/reference_forms.html">Forms Reference Guides</a></li>
                </ul>
            </dd>
                                        </dl>
                                    </div>

oooo sorry…

example