Need scripts: Database search, MYSQL to XML & AJAX show/hide

I need 3 simple scripts. I am developing a web form and I need to INSTANTLY show or hide a div depending on whether a user selects USA for country. Also I need a script to perform a multiple entry search on a mYSQL database & return field ID numbers to be used to display result. I.e. I want people to be able to select Country, City, Business Type, Business Category in the search & have the PHP/AJAX script to look through find and show the rows that match the selected entries. I also need a PHP script to scan through multimedia information stored in a database and produce a XML playlist. I.e. A flash based photo gallery requires xml based file to display images, images are uploaded through CMS & all all image info is recorded in mySQL database. At the time the gallery page is requested the script should quickly look through the database & either append extra photo info at the end of the existing XML file or create a brand new XML file. The script should also be able to save the playlist at a specified folder in the server. (Linux)