The 6600 GT comes in two flavors - PCIe and AGP. Depending on the age of your computer, if this is the PCIe version and you have an older computer (but not ancient computer), you could swap it for the AGP version. If your computer is ancient and does not have an AGP slot, swap it for an nVidia 5500 PCI. In other words, you can't add a slot to accomodate the card. You would have to swap out the motherboard completely.