When trying to call a custom template into your directory you will find the best place to start is with a link that calls the original template for that purpose. For example in your main template and footer template you have links to call individual categories, sub-categories, individual links (via the toplists), member login, member registration, view/edit profiles and logout.

Any of these can be the starting point for calling a custom template. Taking the information from any of these anchor tags and then expanding on it will allow you to call a custom template.

Example:
<a href="http://scripts.webmastersite.net/wsnlinks/wsnmanual410/index.php?action=userlogin">Login</a>
This is the link for members to login, it is located originally in the footer.tpl. If you want to call a custom template for this link you would simply add the code to this link.

Examle:
<a href="http://scripts.webmastersite.net/wsnlinks/wsnmanual410/index.php?action=userlogin&custom=yes&TID=custom-template">Login</a>

Chances are you would probably not be using a custom template for member login, but you get the idea.

Remember that for the categories you also have the option of calling them with the normal link code and adding you custom template information directly to the individual category information.

Also please check out the other custom calling topic's for more information about individual ways of calling things with you anchor tags.