Oh right. I'm sorry.

The kext you are looking for is most likely called NVDarwin.kext

Let me know if you find it.

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Mac OS X Leopard 10.5.7 (Retail)
Motherboard: MSI P6N Diamond
Processor: Intel Core 2 Quad Q6600 2.4GHz
Video Card: MSI NX 6600 TD256E (CI QE Dual Displays)
Memory: Corsair TWIN2X4096-6400C5DHX 4GB DDR2