Add Column to Tarski

There are more than 1000 themes in the WordPress Themes directory. Most people aren’t familiar with every one of them, so a link to your site would help…

I’d suggest that you start by making a copy of sidebar.php and naming the copy sidebar-two.php. Then in each template, immediately before <?php get_sidebar();?>, add <?php get_sidebar('two');?>. You’ll then have to start using CSS float your new sidebar to the right of your primary posts area.

You might also want to have a look at http://codex.wordpress.org/Widgetizing_Themes