Hi Alison
I don't have aardvark post it on my computer in work so the code below is from afterburner, but it may help point you in the right direction. In the layout file (in afterburner it's default.php - but it maybe general.php or frontpage.php or both), you nede to wrap an if(islogged in around the call for the custommenu something like below
<?php if (isloggedin()){ if ($hascustommenu) { ?>
<div id="custommenu" class="javascript-disabled"><?php echo $custommenu; ?></div>
<?php }} ?>
I haven't tested that code and as I said I haven't got aardvark postit on my machine, but hopefully it will give you an idea where to go.
HTH
Richard