Using a disk image is very easy: download the file, mount it through a so-called “loopback” device and your OS will see the image as it was an real harddisk, CDR or DVD. When I needed to test the IDE-drivers, the partitioning-functionality, the ext2 drivers etc, I wanted to use just such an image so I can quickly make modifications and check how the actual structure looked like, just by reading the disk image file. This is a great help when it comes to debugging.