Yesterday, My friend wanted me to do a clean install of Snow Leopard on his iMac(he lost his SL DL-DVD), i was trying to get Snow Leopard(i downloaded it) boot from USB thumb drive with no success, tried verbose mode, and it stuck on loading Extensions.mkext(tried to do some changes to this file, still nothing), and i don't have time to download another image of Snow Leopard, so i decided to use my DL-DVD OEM Snow Leopard of my Macbook Pro, which it works only on my Macbook Pro because OEM are single license-only(if you tried it on another machine you will get "Mac OS X Snow Leopard cannot be installed on this copmuter"), i just need to do some changes to make it work.
It takes time to make modification work on DL-DVD, so i used 8GB USB thumb drive, restored Snow Leopard DL-DVD to USB thumb drive with Disk Utility.
After you get SL on your USB thumb drive, you need to modify OSInstall.mpkg file (which is located on Packages folder) with Flat Package Editor, and to get FPE you have to install XCODE, after that go to
open Flat Package Editor, choose File->Open and open OSInstall.mpkg, you will see Distribution file, drag it to your Desktop(do not close Flat Package Editor, we still need it), and open it with your favorite text editor, Look for the Following:
they are on the line 50052 and 50053, remove installCheckScript() and volCheckScript(), and this is how they should be:
Save modification, and re-drag Distribution file to Flat Package Editor and go to File->Save, that's it, now you should have a working OEM Snow Leopard on any iMachine.