Which plugin? You could have a java applet status bar no trouble at all, not sure how you'd integrate it with php,never tried that shit. I'm pretty lazy so I'd probably just have the php file write to a file to mark it's progress and then the applet reads from that file to display the progress. If your massive searches are going to be database queries I'm really not sure how you;d get prgress reports. AFAIK the DBM recieves the query, processes it and then sends back the result set and that's it.
HTH
Bubble
