Which PHP file generates the catagories in the catagories side box?

I’m trying to achieve this style of menu;
http://www.jameschetwood.com/menu/menuiwant.jpg

I want the sub menu to open after you click on the link in the main menu. When you click on the link in the sub menu, you are taken to the products page, and the menu stays ‘extended’ to work as a landmark.

As I need the menu to stay ‘extended’ when you are on the products page, I decided to modify the categories side box, rather than the CSS fly out menu.

I made the categories side box the only side box in the right column, then turned off the display of the right column.

I then made the categories side box appear below the header by putting the following;
<div class="test">
<?php require(DIR_WS_MODULES . zen_get_module_directory('column_right.php')); ?>
</div>

above this;

In tpl_main_page.php

I’ve removed the styling with CSS and the div’s ID and made the categoriesHeading div not display. You can see how far I’ve got here;
http://www.jameschetwood.com/menu/catagoriessideboxmenu.jpg

To make the categories side by side rather than on top of each other I now need to edit the php to remove the <br/> from each category AND/OR make each category generated in a separate div so I can control the layout that way.

Where is this PHP file located?

thanks
james

Ok, made some progress (i think).

Ive edited
mysitename/includes/templates/mytemplatename/sideboxes/ tpl_categories.php

  case ($box_categories_array[$i]['top'] == 'true'):

    $new_style = 'menlev1';

    break;

  case ($box_categories_array[$i]['has_sub_cat']):

    $new_style = 'menlev2';

    break;

  default:

    $new_style = 'menlev3';

  }

the only thing ive changed so far is the names of the divs to menlev1, menlev2 and menlev3.

If I start removing page breaks then the divs can be aligned horizontally, but the main page content goes up to high. Where would I add a clearBoth div so it was at the bottom of my menu?

Im also predicting problems for a 3 tier menu (at the moment im only working on 2) as menlev1 is the top most category and menlev2 and menlev3 control the second layer. How would I control a third layer if I had one?