Accordion / collapse - expand menu for marketpress product categories

Hi,

I'm not entirely sure if this is the correct place to post but I had to post somewhere. If you take a look at the product menu at http://www.mobilityproducts4u.org you will see that there are top categories and sub categories. They are all expanded which results in a very long menu. It's too long. What I would like is to have all the top categories collapsed and for them to open out when clicked on without the need for a page refresh. Ideally it would also be set so that only one top category is expanded at any given time so clicking on a second top category would cloose the first.

Hope that makes sense. Any idea or suggestions?

Thanks

Daniel