To have a custom template load instead of the normal template for that purpose, you need to make changes to the anchor tag that will be calling that page. In the anchor tag you will need to add the following information: custom=yes&TID=nameoftemplate.

Here is an example:
<a href="http://scripts.webmastersite.net/wsnlinks/wsnmanual410/index.php?action=userlogin&custom=yes&TID=nameoftemplate">Login</a>

There are a number of other custom calls you can make within you anchor tags in order to customize your directory exactly to your tastes, please check out the other manual items for more information.