There are 2 ways of using Norton Ghost:
1. to make a backup image of a drive
2. to clone a drive
Making a backup image leaves a file with a .GHO extension on a disk. You use Norton Ghost again to restore that image back to the drive it came from. It is a total back-up of the drive. It does not affect the other contents of the drive on which you make the Ghost image..
Cloning a drive means making an exact copy of the drive. You might want to do this to set up 2 or more pcs identically if they have the same motherboard etc; it is easier than installing XP from scratch on multiple pcs if you have multiple licences. Cloning a drive wipes out any data that may have been on the drive being written to.
It sounds as though what you have done is clone your drive rather than back it up. In theory, i your main drive fails, just take it out and replace it with the clone.