Re: Parent- & Sub-Category Dropdown Menus
ClassiPress uses the
wp_list_categories function
Your customization would take some work more on the backend and deciding how you'd like to save the 2nd category listing. The current category dropdown uses the standard wordpress category functionality which is easy. It's the 2nd dropdown you'd have to create a custom field for since it WordPress can't handle it natively.
You would need to create another wp_list_categories function and use the "child_of" parameter set to 1 (i believe) which will only show sub-categories.
Then modify the current wp_list_categories function and use the "depth" parameter set to 1 to exclude sub-categories.
You'll then need to edit the post_form.php file and save it into a new custom field. Then add it to the appropriate places to display on the pages.
If you aren't good with coding, I recommend you hire someone to do this mod for you.