You can download the driver form the Realtek's official website. Access the website and wait for the page to load, then click on the driver for Windows XP. The driver's version is 5.719. Use the download link close to your region to have maximum downloading speed.
To install it, download the package and run the setup. You might need to use another computer to download the driver if you don't have an active Internet connection on the computer with the PCI card.