The CentOS team has released CentOS 3.4 (Final) for the s390 architecture. This product supports IBM S/390 machines.

This release includes all updates and errata up to February 11th, 2005.

This release is available via Bittorrent (as a DVD) from the following location:
http://mirror.centos.org/centos/3.4/isos/s390/centos-3.4-s390-bin.DVD.torrent

If possible, please use bittorrent to download all files and please leave your download client running after the download is complete (with ports 6881-6889 open) as your client will become part of the peer to peer bittorrent network and reduce the load on our network mirrors. If you need some quick pointers for getting up to speed on bittorrent read:
http://www.centos.org/modules/smartfaq/faq.php?faqid=24