Display Subcategories on Category Pages

I am adding the following code to my archive.php file...

<<<BEGIN>>>
<?php
if (is_category()) {
$this_category = get_category($cat);
}
?>
<?php
if($this_category->category_parent)
$this_category = wp_list_categories('orderby=id&show_count=0
&title_li=&use_desc_for_title=1&child_of='.$this_category->category_parent.
"&echo=0"); else
$this_category = wp_list_categories('orderby=id&depth=1&show_count=0
&title_li=&use_desc_for_title=1&child_of='.$this_category->cat_ID.
"&echo=0");
if ($this_category) { ?>

    <?php echo $this_category; ?>

<?php } ?>

<<<END>>>

It works great, but I want it to only display when a particular category is being viewed. Can you help me?

http://policyandtaxationgroup.com/category/estate-tax-horror-stories/

Or, if you have a better suggestion for displaying sub-categories on a category page, I am open to it?

Or, is this better done now-a-days with a shortcode? If so, what plugin do you recommend?