Mac OS Leopard damaged; I created a dmg of the HD before formatting?

Huh? I can't imagine any possible way to use your external drive for anything at all if there is no operating system on this computer. Which computer is it? When you say "Mac OS Leopard damaged", does that mean you made this DMG of the damaged Leopard installation? Do you think it will get undamaged? If it can't get undamaged, I am sure you are wasting your time hoping to restore it to the hard drive. If it can get undamaged somehow, read on...

If you formatted (I think this means erased) the hard drive, where is this DMG? If the DMG is on another Mac, you can start the OS-less Mac while holding the T key for 18 seconds. That will put it in target disk mode. Connect the OS-less Mac to the other Mac by Firewire cable. If the other Mac is a new uni-body MacBook or a MacBook Air, this isn't possible. You will need to get your hands on a Firewire equipped Mac. Open Disk Utility, open Disk Utility Help, and search for "restore". The restore process will copy the DMG data (visible and hidden) to the hard drive. When that's done, restart the once OS-less Mac. Look at the files of the hard drive in a Finder window. Do you see folders named etc, tmp, and var? You shouldn't. They should be hidden, but the restore process is faulty.

If you see etc, tmp, and var on the newly restored hard drive, insert your Mac OS X 10.4 installation disc. Open Terminal and type the following commands, each on one line:

cd /Volumes/Mac\ OS\ X\ Install\ DVD/

Press Return.

or for a 4-CD set: cd /Volumes/Mac\ OS\ X\ Install\ Disc\ 1

Press Return.

cd System/Installation/Packages/

OSInstall.mpkg/Contents /Resources/

[I made a line break after "Packages/" because the forum has a 30 character "word" limit that truncates long, unbroken text -- type those two lines of code as one, no space after "Contents". For other lines of command, the spaces are appropriate.]

Press Return.

sudo ./SetHidden / hidden_MacOS9

Press Return.

Quit Terminal, log out, log in (or restart).

EDIT: Now I get it. You have already installed Tiger; you just wish you had Leopard back. You can't permanently mount a disk image. You can copy all the files to a folder. If you are wishing to make the Leopard image bootable, you can restore it to another drive volume that is data-less. For example: copy the disk image to the internal hard drive, erase the external drive, use Disk Utility to "restore" the image to the external drive. Even then, as I mentioned above, it should be an image of bootable data in the first place or you would be copying faulty data. Also, if the external drive connects by USB, the system will run very slowly when booted to it. Firewire external drives make a reasonable startup disk, as FW400 is about 3 times as fast as USB 2.0 in such circumstances. If the enclosure is USB only, consider buying a FW enclosure for much improved performance whether you will boot from it or not.

This document format is in this type of a Mac OSX Disk photograph. you need to transform the .dmg to .iso. the utility for changing is given below. set up the utility and then convert the disk photograph and whilst that's converted to .iso burn it onto a dvd employing any burning utility like nero,etc.