All you really need in your new file is:
{capture name=menu}
{foreach from=$categories item=c}
{if $c.order_by gt 900}
<font class="CategoriesList"><a href="home.php?cat={$c.categoryid}" class="VertMenuItems">{$c.category}</a></font><br />
{/if}
{/foreach}
{/capture}
{include file="menu.tpl" dingbats="dingbats_categorie.gif" menu_title=$lng.lbl_categories menu_content=$smarty.capture.menu}