If your computer is about 4 years old, it's not going to have a PCI-E (PCI express) bus on it. So you're going to have to go with a graphics card that is either AGP or PCI. You really shouldn't have to spend much money, or even go with the latest stuff. A PC that old will likely hinder the performance of any of the latest cards with lots of horsepower in them. If you have more detailed specifications of the PC I could probably recommend something more specific.