Thanks for the reply.

I've never modified the GPU bios from factory settings, and PCIe is set at Auto in the BIOS, also I am not OCing the CPU.

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System 1: Gigabyte GA-P35-DS4 MB with Intel e6750 Core 2 Duo w/8 GB RAM (Retail install)
GeForce 8800GT 512MB, Snow Leopard 10.6.2
System 2: Dell Optiplex GX280, Intel P4 3.0Ghz w/3GB RAM
GeForce 7800GTX 256 MB, Leopard 10.5.7 using iATKOS v.7 install (work in progress)