As with any component, you have to look into compatibility. Make sure to pick the right type of card for the slot(s) on your motherboard (either AGP or PCI Express), and one that is physically small enough for your computer case. It is also possible to get too powerful of a drive for your current processor and power supply, which could harm rather than improve your gaming experience. If you have an older machine, it probably can't take the latest and greatest graphics card. A nice midrange card can greatly enhance performance for a couple of hundred dollars, but you can also find much cheaper ones that aren't bleeding-edge that will suit your needs just fine. Some motherboards also support running identical video cards in tandem to boost performance