Umn I am not exactly sure of what you are asking, but based on what you just wrote out, you have an older generation GPU, something like a 5 or a 6 series card from Nvidia or a 9 series card from ATI. Fortunetly this means that you should have a PCI-e x16 1.0 slot. If this is the case, you can pick up a lower end card, like a Geforce 430 or a Radeon 6450.
Now this all just a guess based on the vague information you gave us. To be more specific, we need the type of motherboard as well as CPU that you have.