BackTrack is a boot CD, known as a live distrubtion. This allows the user to boot there PC, server, or Intel based Apple MAc into a Linux OS from the CD, regardless of the operationg system already installed on the computer.
BackTrack is based on a Slax, and full of pen-testing/ethical hacking tools. Its a complete CD of everything you need, and it all remains in RAM, rather than being stored on the hard drive, it leaves no evidence. This makes the tool excellent for the incident response team, and hacker alike. It has all of the imaging functionality with DD, that is expected of similar tools such as Helix.
In addition to providing an ISO image, BackTrack also comes ready for use on USB and with a virtual hard drive. The format is VMDK, for WMWare, but users of VirtualPC can convert it to a VHD using the following converter