top-search input box

I'd really like to attach a drop-down list to primary nav top-search input box and then populate it with items from my typeahead widget - obviously I only want to show the dropdown when the top-search box is showing. Is this easy to do. I've not been able to work it out.
Many thanks
MattyP

I have the same request, it would be an excellent enhancement as in many sites the search box is essential.