VirtualBox: Mac OS X 10.5.8 Guest on Mac host with Core i7 processor

The Leopard 10.5.0 Retail DVD booted and installed perfectly using VirtualBox 4.0.12 on my MacBook Air. After applying the 10.5.8 combo updater, unfortunately, the VM would kernel panic while booting. The culprit was the AppleIntelCPUPowerManagement.kext. The 10.5.8 kext doesn't seem compatible with Core iX processors.

The solution is pretty simple, and clears up another well-known problem as well: 100% usage of one core at all times:

1) Boot the VM using the 10.5 Retail DVD and launch Terminal
2) Delete the offending kext:

rm -rf /System/Library/Extensions/AppleIntelCPUPowerManagement.kext

3) Reboot and enjoy!

The post that tipped me off to this solution also suggested installing a dummy kext, however I could not locate a 10.5.8 compatible NullCPUPowerManagement.kext. I skipped that and have not noticed any ill effects.