392173 Category Customization Needed

I am new to scriptlance and in search of a php/html/mysql coder that can help me customize my existing membership script.. This will be a one project of many. Please check out my site here [login to view URL] Under the admin settings of the script there is a section where can add categorys. At the moment I can only get to choose a main category. I would like this to be changed so that I can add sub categories (if needed) to them. On the add/edit pages I will need to show the new sub category as well as the main categories. Also on the add/edit pages at the moment I can only assign the product to one category at a time. I wish to make this so that I can choose multie categories. On the actual layout side I need to show the sub catgories under the main categories.. can they appear something like this, main categories are shown first, then you click on one the sub categories are shown?