I am not familiar with the vb3 but I will show you how it is done in vb 4 and then you can follow the example with some adjustments in conditionals and template variables.
At the memberlist template I add <vb:if condition="!$show['guest']"> just under the {vb:raw navbar} then all the way towards the bottom I close the condition. i.e the following <div id="pagination_bottom">
{vb:raw pagenav}
</div>
</vb:if>
is changed to:
<div id="pagination_bottom">
{vb:raw pagenav}
</div>
</vb:if></vb:if>
Have a look at the memberlist template of your forum and follow the example I posted above but don'''t forget to adjust the conditional and the template variables which from what I have seen it is different in both versions.
If you still can''t do it, then post here the memberlist template and I will make the edits for you.