Get PC-EFI v9, put it on a USB stick. Boot from CD, and install the bootloader manually. After you have the bootloader installed, you should be able to boot normally, provided your system is able to run a vanilla kernel.

If it can't you can install the Voodoo kernel manually too, and specify that kernel at the prompt. Once you are up, you can make permanent changes and fix your startup.

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Apple Macbook Pro 15" 2.93GHz | Apple 24" LED Cinema Screen

iAtkos v5i 10.5.6 Vanilla

Machine: Acer 7730G
Memory: 4GB DDR2/667
Storage: 2x 250GB
Display: nVidia GeForce 9300M GS