Norton Ghost is one of several programs that will create an image of a hard drive (or a partition on a hard drive). An image is similar to a photocopy - it makes an exact replica of your hard drive onto another drive.
Using this sort of program, you can take a snapshot of your drive at regular intervals - if anything goes wrong with your system, you simply reload from the image, and you are back to a working system in tens of minutes, exactly as you were the last time you imaged your disk.
There is one 'gotcha' - you cannot store an image of a disk (or partition) to the same disk.
Therefore, you need either two hard disks, or a single hard disk split into at least two partitions.
Is it worth buying? If you value your data, it is one very simple method of backing up your data. Like all backup strategies, it is only of any value if you actually carry it out regularly.
Go to symantec.com to find out more.