Ajax Filtered Search

Hi there, I need to develop a page that has a search form, containing a series of dropdowns to filter the search results. I would also like to use some ajax so that the results will appear below the form, rather than going to a seperate page.

It would function something like the ‘Find Used Cars’ form on the left of this page: http://www2.autotrader.co.uk/

I will be using it to search for products, so each product will have the fields completed in order to make selections from the search dropdown fields.

I was wondering if anyone has done a form like this before and might be able to share some tips or modules which have been used.

Thank you.