After a few agonizing days of attempting to set up some very custom category displays for a client, we are posting the results here in the hopes it might prevent some other poor programmer from gaining the very same forehead dents we currently sport.

(Note: the following was accomplished in a MT 3.34 environment)

The requirement: List subcategories for one single category in Movable Type.

The solution:

First, install Staggernation's FilterCategories plugin.

Second, set up your categories, subcategories, etc., then use this code to call them:

<MTTopLevelCategories>
<MTFilterCategories include="Category">
<ul>
<MTSubCategories>
<li>
<a href="<$MTCategoryArchiveLink $>">
<$MTCategoryLabel$>
</a>
</li>
</MTSubCategories>
</ul>
</MTFilterCategories>
</MTTopLevelCategories>

Adjust the display mechanism (ie. ul, li, etc.) as you like and there you go.

You can see it in action on the From ABBA to Zeppelin, Led blog, in the right hand sidebar.