At present, the article filter in joomla 1.5 only searches the article title to filter the results.

I need the filter to search the article description as well as the title to filter the results.

To see an example of the page in its current state, go to:
http://guidetocanberra.com.au/mitchell/auto

The page that contains the filter box code is:
templates/ja_purity/html/com_content/category/default_items.php

I also need to replace the filter input box with a dropdown box. The visitor will be able to select an option from the dropdown box to filter the results. The options in the dropdown box will need to be added through admin or simply by editing the form in the php file.

Let me know if you need more details or clarification.