Upgrade from Leopard to Snow Leopard, 10A432?
It can be upgraded from 10.5.7 to 10A432.
Try to install Existing Leopard Hard Disk. It just upgrade from 10.5.7 to 10.6.0
Then update 10.6.1 by software Update.
But, you have to replace Sleepenabler.kext from Netkas' site when you update to 10.6.2.
It sometimes did not working GFX-String in 10.6.2, especially nVidia 7xxx series, 8xxx series.
if you have black screen after booting followed by lord_webi's guide.
delete following prefs/plists if existing in directory (boot with -x):/Library/Preferences/ByHost/com.apple.preference.display*/System/Library/Preferences/ByHost/com.apple.preference.display*/Users/YOURUSER/Library/Prefereneces/ByHost/com.apple.preference.display*same to *loginWindow* prefs/plists ... in all that directories if existing ...restart and your EFI string will work again ...