I don't have any fresh ideas about the lines using the internal VRAM. However, if you have VRAM installed and install a PCI video card the PCI card is a secondary monitor, so the 8600 boots to the internal VRAM and you see nothing because there's no monitor connected. You need a monitor connected to the internal port to swap monitors around via the monitors control panel. As per the previous suggestion, connect two monitors and proceed.

At least that's the way my 8600/300 behaves.