If you just want to hide stuff from view then you could use something like :-

<style type="text/css">
.members_only{
display:<?php echo ( is_logged_in() ? 'block' : 'none' ); ?>;
}
</style>

............

<div class="members_only">
<p>Yay you're logged in!</p>
</div>

If you want to actually remove it from the source then you'd need to create a renderer plugin that hooks into [url=http://doc.b2evolution.net/v-1-9/plugins/Plugin.html#methodDisplayItemAsHtml]DisplayItemAsHtml()[/url] and performs a similar test and either allows the html or removes it from the source.

¥