a very simple way is to use Ajax to get progress information.
You could for instance use DynAjax framework (visit dynajax.org) and implement a server method that returns the progress percentage (0 from 100) according to the current Thread search.
With DynAjax, call server method via JavaScript and get you progress method in order to update progress bar display.
Of course, you should get a dynamic progress bar displayed and controled by JavaScript.

Hope it helps.
MagicBen.