The NVIDIA Leopard kext installers updates system kexts with nvidia official drivers (from Apple), they should not be needed for your card, its more useful if you have recent cards like 9600/9800.
The injector kexts (nvkush, nvinject, corevidia, etc.) make your nvidia card look as it if were a real mac card. You can use one but only one of those injector kexts. Make sure you dont have more than one installed in /System/Library/Extensions at the same time.
You need both things to get QE/CI working, a working set of nvidia system kexts (they are installed by default with Leo) and one injector kexts that supports your card.

The starting problem is different, it means the bootloader needed to start leopard didnt get installed properly, you can try to reinstall it from the iAtkos DVD (selecting the bootloader only) or just boot from the DVD and install the Chameleon 2 installer.

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AsRock P45TS | C2D E8200 | GeForce 8600GTS
Mac OS X Snow Leopard 10.6.1 + Windows 7 Ultimate 6.1.7600 + Fedora 11