It took me a while to figure this one out. The Zen forum contains a more elaborate solution that includes removing a sidebar from the category pages as well as the product description pages. I just wanted to remove the sidebar from the product description pages. So far, this seems to work fine for me. I thought I’d share it with you.
Simply copy and paste the code below as the first line of your PHP code on the /includes/templates/YOUR-TEMPLATE/templates/tpl_product_info_display.php page.