Backtrack is a LiveCD Linux distro developed for security system penitration testing. The CD contains many advanced security-orientated tools.
Remote-exploit offers training in using Backtrack Linux for security evaluation.
Official Backtrack site http://www.remote-exploit.org
Backtrack is not available on the SUN FTP server yet.
Backtrack 4, the latest release, available from the remote-exploit website.
Backtrack 3, just an email (and some chocolate/biltong/beer) away - firstname.lastname@example.org
Site in development, please be patient as perfection takes time.