Tanzaku theme – single post tweaking

Because the Tanzaku theme — http://ww.wp.xz.cn/extend/themes/tanzaku
— doesn’t have a separate single.php file, it simply uses javascript to throw the single file on top of the loop, as I understand it, the single page needs some tweaking.
What i want to do is the single post appear separately without the top sidebar, and the header, and ideally want the posts file underneath that belong to the current post category.
How to achieve this?
— where do I remove the pesky top sidebar from the single page?
(is it on the main index template or maybe functions file?)
–how do I tweak this little code to show the category posts appear below the single post?

<?php /* make a new query for grid items (in single page) */
$new_query_arg = ‘paged=’.$paged;

// use this code if you want filter items by category.
/* $arr_catID = array();
foreach( get_the_category() as $cat) $arr_catID[] = $cat->cat_ID;
if ( count($arr_catID) ) $new_query_arg .= ‘&cat=’ . join(‘,’, $arr_catID);
*/

query_posts($new_query_arg);
?>

I am not a coder, so I am afraid to change the code and don’t know how to make it right.

Thanks.