I think your talking about flushing the current output to the browser, you need to use output buffering and then flush it to the browser.
eg.
PHP Code:
<?
if (ob_get_level() == 0) ob_start();
for($i = 0; $i < 10; $i++) {
echo "<br/>$i"; // your output
ob_flush();
flush(); // needed ob_flush
usleep(50000);// delay minimum of .05 seconds to allow ie to flush to screen
}
?>