Well I just installed 4k73 last night successfully. It was a toast image, just lock the image in the get info panel and double click and that should open up toast and automatically be ready for you to write it to a disk. Once it's done burning then you should be all set, unless you downloaded a bad image
Most of the problems with downloaded Mac OS X install images relate to mounting the image before burning them. Don't do it. Just download it and burn it. Once you mount it, even just one time, you won't be able to install it anymore.
The problem has to do with desktop database or something like that. I read about how to fix it once, but I can't remember where (and I have been looking for it, believe me).