Your best option is to use a program such as Acronis True Image. This will let you either "clone" your hard drive, or create an "image" file which can be restored to your main drive in the event of problems with the installation or restored to a new drive in case of main drive failure.
Cloning is normally only used if replacing a drive that may be failing or when upgrading to a larger drive. Creating image files means that the rest of a second hard drive can still be used for normal file storage.
For a free program that will create an image file of your entire hard drive, have a look at Macrium Reflect, although in the free version, you need to boot with the CD (which you create) to perform the "restore" operation.