Your Graphic Card make & model is listed in the Device Manager.

Or you can download Belarc and it will provide a detail audit of your computer hardware & software.

Once you have identified the make & model go to the manufacturer's website and download and install the latest drivers.

You did not mention if your XP has SP2. If SP1 you might also need to download DirectX9c which will improve the performance of your Video Card.

And if you have an ATI Radeon the latest driver will require you to download Microsoft .Net Framework.