How to create two select dropdown menus that are related

I tried the CF_twoselectsrelated but it is supposing you only have 1 query.

I have a query that selects categories and another one that selects subcategories - maybe that is where I am going wrong. the queries are:

SELECT
        T_categories_ID
        ,T_categories_name as categoryname
    FROM
        T_categories
    WHERE
        T_categories_ID > 0
         AND
        T_categories_subcat_ID = 0
        AND
        T_categories_active = 1
        AND
        T_categories_partnerID =  #session.partnerid#
    ORDER BY T_categories_name ASC

And the other one is

SELECT
        T_categories_autoid,
        T_categories_subcat_ID,
        T_categories_subcat_name as subcatname,
        T_categories_subcat_description as description,
        T_categories_subcat_img, T_categories_imgname
    FROM
        T_categories
    WHERE
        T_categories_partnerID = #session.partnerid#  AND
        T_categories_subcat_Parent = #attributes.categoryID#
    ORDER BY
        T_categories_ID,
        T_categories_subcat_name ASC

The categories and subcategories are in one table (was not my idea:-))

Please can anyone point me in the right direction??

Bianca