Ghost can be used to make a backup image of your drive partitions that you can use to restore later. Depending on the version of Ghost you have, you can also have the image to span across mulitple CDs if writing to the hard drive is not possible.
For example, I always make a Ghost image of my C:\ drive once I have WinXP, Windows updates, drivers, and applications installed. That way, if I need to reformat later, it takes 10mins to restore the Ghost image, instead of the 3-4hours of installing the items individually.
It basically takes a "snapshot" of the drive that can be restored fully.