Creating dragging functionality with JS and JQuery

Our website has a tree structure of categories (imagine browser bookmarks tree structure style, Category inside another category and etc.) and we would like to rebuild the dragging functionality of it. CSS and HTML part is ready, only JS is required to be done. Functionality that has to work: 1. Possibility to drag a category and to put it on top or bottom of another category or inside another category. 2. When dragging a category and hovering on top of another, it should open the category after 0.5 seconds (make the subcategories visible) 3. Same as 1 just for subcategories Only someone who is available at least couple of hours a DAY. We will be working via Skype.