Timeout while waiting for a server->client transfer to start (large files)

Hey I have a script that I am trying to figure out to allow a remote file to be sent to a client's browser. It works ok for small files, but it keeps timing out for large files. I don't think it should even take as long as it does (i.e. about 10seconds) before it pops up a dialog box for me to download a 700KB file. Any ideas? It times out on a line around which reads while (!feof($fp)) {

            $tmp .= fread($fp, 64);

} Thanks ;)