Oscommerce filter by category then by size

Hi, this project is basicly to add filter drop downs to my website, my website is based on OSCOMMERCE V2.2 RC2a My online store is a fashion store. 1. after vistor clicks on any product category or sub-category, I want to have a drop down filter on the top of any product listing page to enable user to filter products under the selected category by Size (which is the only attribute used). 2. on the home page, have 2 drop down filters, first drop down has a list of all products categories & sub-categories & second drop down has the different SIZE options for users to choose from. users can choose a category from the first filter then a size from the second filter then hit SEARCH button to go directly to their desired category & size that they choose. I have a mirror domain that all the untested work will be done in it first & after installation & after successful testing the work will be moved to the live website to eleminate any downtime. Thanks