You need to create a "Disk Image" which is essentially a large file which contains all the partition information, folders & files of the drive you've created an image of.
If you're running Windows 7 it already has this capability built-in.
Control Panel >> Backup & Restore.
If you use that method, don't forget to create a "System Disc" as well so you can boot from it to perform a restore from the image.
If you don't have Windows 7, there are several third-party applications which do the same thing, but I can only the recommend the one I trust:
Active@ Disk Image: http://www.disk-image.net/
Although I do have Windows 7, I prefer to use Active@ Disk Image because it's much more versatile than Windows Backup & Restore.