[CentOS] minimize download bandwidth techniques

I know of a few techniques for minimizing server bandwidth when
bittorent is not an option.

1) If you have the beta isos, you can rename them as centos 5 isos and
then rsync from a mirror that allows rsync (such as kernel.org).  Then
only changes from beta to centos 5 plus some overhead is downloaded.  I
suppose you could use this technique with bittorrent too.

2) Instead of downloading both cd and dvd isos, just download the cd
isos and use a script to create the dvd iso.  You can rsync like step 1
if the dvd md5sum differs.

A cd to dvd script is at url below (although I haven't tried it yet).
http://www.tuxforums.org/forum/viewtopic.php?t=446