by "the block" do you mean the "don't want javascript" block? do this:

<script>
javascript menu generating thing
</script>
<noscript>
html alternative
</noscript>

otherwise;have an element:

<div id="javascript_please_hide_me">
put your html alternative here
</div>
<script type="text/javascript">
document.getElementById("javascript_please_hide_me").style.display="none";
</script>