triggering php scripts...

hello, i am wondering if there is a good way to trigger a php script from a web page *without* sending the user to a new page or opening a new browser windows. for instance, suppose you wanted to make a button/link on a web page that, when clicked, would cause a database entry to be decremented. however, you do not want to refresh the page or open a popup window or any stinky little tricks like that. or, if this is not possible, does anyone know how to trigger a php script when someone accesses a particular file from an apache server? or if a file from a particular directory is downloaded... thanks a lot!