the download script can only download remote files to the local server on which the script is running, so what you have to do is put the script on the server where on which you want to download the files. This is in your case the remote server.
Then, when the script is working OK, you access it from your own server using for example fopen.
REMOTE SERVER A:
LOCAL SERVER B:
download.php contains the script that does the downloading:
if (download("http://SERVER B/uploaded_files/".urldecode($_GET['file']), "images/".urldecode($_GET['file']))
activate.php is the script that you trigger after the file is uploaded and does the following:
fopen("http://SERVER A/download.php?file=".$_FILES['file']['name'], "r");
in this situation i've assumed that all the uploaded files are stored in the dir /uploaded_files
check also http://www.php.net/fopen to see how to retrieve the response Yeah! or Damn