That is an old system. Does your model have a stand alone video card or is it integrated (the video) into the motherboard?
That being said, your options for either are VERY limited given the age of the system. I am hoping you have one of the 4600 series with an AGP slot. If so, we can find a solution. If you have the integrated solution, you will be stuck with what you have (in terms of changing video adapters).