Index: upload.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/upload/upload.module,v
retrieving revision 1.197.2.1
diff -u -r1.197.2.1 upload.module
--- upload.module	11 Feb 2008 15:08:09 -0000	1.197.2.1
+++ upload.module	16 Feb 2008 14:36:26 -0000
@@ -154,6 +154,7 @@
     return array(
       'Content-Type: '. $file->filemime,
       'Content-Length: '. $file->filesize,
+      'Content-Disposition: attachment; filename="'. mime_header_encode($file->filename) .'"', 
     );
   }
 }