Originally Posted by Taisto

There You go :

Before you start : Download Andy's 9.6.0 kernel package. search the forum for link.

1. Open the terminal.
2. Browse into main directory of your Mac OS partition.
" cd /Volumes/name_of_partition "
" ls -l "
3. You should see a file named "mach_kernel" there. Make a backup of it.
" cp mach_kernel mach_kernel_old "
4. Repair its permissions.
" sudo chmod -R 755 mach_kernel_old "
" sudo chown -R 0:0 mach_kernel_old "
5. Now you can run Software Update, and get your update.
6. After the update - restart your computer.
7. While booting, press F8 and write :
" mach_kernel_old -x "
8. When your computer boots up in safe mode - just install Andy's package.
9. Restart and boot normally.
10. You have 10.5.7 running.

Well, that's it. You can of course make a backup of System.kext aswell, then instead of booting into safe mode and installing Andy's kernel - you can boot into -s mode and copy back the System.kext ( and repair permissions ), but i find this way more convenient.

PS. seatbelt.kext is needed on 10.5.6 to mount USB/DMG properly. Without it your system may fail to mount usb drives or images, or kernel panic at you when you try to do it.