Look at how they did it in the default navbar template. Here's the link in the navbar:
HTML Code:
<td class="vbmenu_control"><a id="usercptools" href="$show[nojs_link]#usercptools" accesskey="3">$vbphrase[quick_links]</a> <script type="text/javascript"> vbmenu_register("usercptools"); </script></td>
You need to modify that to have an image and put it in place of all the stuff inbetween these lines:
HTML Code:
<td width="78"><img src="/images/gradients/hbf/10.gif" border="0">
<div class="vbmenu_popup" id="usercptools_menu" align="$stylevar[left]">
<table cellpadding="4" cellspacing="1" border="0">
stuff
</table>
</div>
</td>
And then put all that stuff at the bottom like in the navbar (with display:none).