how to use function arg() in drupal to call .tpl files? I have 3 .tpl files, how can i call these tpl files by using function arg().
 actually i want to show 3 different .tpl files to user when he request from a dropdown options.

The detail description is i want to create a page which render list of nodes in a page but i like to give option to user that weather he wants all the node in single column layout or 2 column layout or 3 column layout. For these layout i'm creating 3 different .tpl files so now i want to call them on the request of dropdown list.
If I understand it correctly you are looking for a way to render .tpl.php files on certain paths, this article explains how to do it. 

In the article they define only one path and show you how to make sure a .tpl.php is rendered. You can easily adjust the code to make it work with 3 different paths and 3 different tpl.php files.

Hope this helps!