In order to conserve the limited bandwidth available .iso images are not downloadable from this mirror.
Please use a public mirror listed here instead.
Or use bittorrent to download the .torrent files provided.
Bittorrent is a peer to peer download system described at http://bittorrent.com/ and there are many clients available.
These include (in no particular order of preference): utorrent, vuze (Azureus), BitTorrent, Deluge, ctorrent, ktorrent, rtorrent and transmission.
Packaged copies of various torrent clients for CentOS can be found in the repositories listed in the following wiki article : http://wiki.centos.org/AdditionalResources/Repositories