Multiple Select Dropdown List

Hi,

I have over 2300 products with many categories and sub-categories. I'd like to be able to browse through products using Multiple Select Dropdown lists like this one: http://www.coursesweb.net/ajax/multiple-select-dropdown-list-ajax_t.

This Search/Select could be at the top of the Products page for instance, or in a sidebar.

Do you have any pointers on how to do this with Marketpress ?

Thanks !