Load OSX 10.6 on external HDD and boot for re-install of OS?

Heres the issue...I have an iMac Intel Based early 2006(original intel model)...my dvd drive stopped working and now i need to re-install my os....I have a backup of my OSX 10.6 in a DMG file, and a 320GB external HDD, i want to be able to boot my imac from the external hdd and reload my os...unfortunately i didnt backup with time mach......SOMEONE PLEASE HELP.......i have tried many suggestions from many sources online, and have had no luck...i have access to a high end PC with windows 7 and i also have Ubuntu Live CD, WHAT CAN I DO WITH WHAT I GOT