Chosen Solution

Good morning (in Italy!) :)) I have a Mac Pro Early 2008 (3,1) 2x2,8 quad core cpu. It came with two ATI Radeon HD 2600 XT 256 MB graphic cards installed. Now i bought a Nvidia Quadro FX 5600 1,5 gb. To install this, have i to remove the two ATI or just one of these? Which slot pci-e should i use? Sorry for my poor english, and thanks in advance.

You just have to remove one ATI, doesn’t matter which one you remove. Use the remaining PCIe slot for your nVIDIA.