No, my mod is not quite like that, if you want to see it:
http://www.mindells.com/home.php
and then click on the Pumps category, that is how MY submenu will work. And I am also integrating a 'Browse by Brands in this section' type submenu into it also.
It looks to me as if you need to just pull the JAVA information from the template that the 'Browse Store' area is located, and place it into the 'Menu' template, modify it to drop out instead of down, and to pull subcategories instead of 'by type' and by 'brand', and you should be set. I know I make it sound fairly simple, but I really don't think you should be having as much of a problem as it sounds.