Index: upload.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/upload/upload.module,v
retrieving revision 1.184
diff -u -r1.184 upload.module
--- upload.module	10 Oct 2007 10:24:25 -0000	1.184
+++ upload.module	10 Oct 2007 14:18:04 -0000
@@ -154,6 +154,7 @@
     return array(
       'Content-Type: '. $file->filemime,
       'Content-Length: '. $file->filesize,
+      'Content-Disposition: attachment; filename="'. mime_header_encode($file->filename) .'"', 
     );
   }
 }