flushing contents to the browser

hi folks, i'm trying to display something like "processing... please wait" on a web page whilst a rather hefty database query is being run. i don't want to refresh the page so i've been attempting to use flush and ob_start, together with some css stuff to try and do this.. but no luck so far - as once the buffer has been flushed, i can't retrieve the content.. does anyone have any nifty ideas? many thanks dk