First of all extract your theme into a folder and open it to see all the files.

If your theme has only one sidebar, then most probably you will NOT find a functions.php file in your theme  folder. In that case you will have to create this file yourself.

Create a new blank functions.php file or open existing file and put this code into that file:-
<?php
if ( function_exists(’register_sidebars’) )
register_sidebars(2);
?>
These lines of code actually tells Wordpress to register two sidebars for your theme . If the functions.php file already present in your theme folder then you just have to edit the number according your requirement and save the file.

You can change this number if you want more sidebars. Now, when you go to your Wordpress admin section, you will see two sidebars listed there. You can drag your widget items into any of the sidebars.

Now If your theme has only one sidebar, try to locate a file called sidebar.php in your theme folder.
we are trying to modify the theme for two sidebars, let’s rename sidebar.php to sidebar1.php and make a new blank file called sidebar2.php.
Put this code into sidebar2.php and save the file :-
<div>
<ul>
<?php if ( function_exists(’dynamic_sidebar’) && dynamic_sidebar(2) ) : else : ?>
<?php endif; ?>
</ul>
</div>
Both these sidebars need to be called from the index.php file in order to include them in your theme.

In your index.php file search <?php include (TEMPLATEPATH . ‘/sidebar.php’); ?>
Edit this code and change the words sidebar.php to sidebar1.php.

Now take a look at the index.php file carefully and find a suitable place to insert the second sidebar. This might involve modifying your layout or adding new divs. Once you find a suitable place, place the following code there :-
<?php include (TEMPLATEPATH . ‘/sidebar2.php’); ?>
Save the index.php file and now preview your theme.