Go to the vendor’s website to get the latest supported drivers. However no specific drivers for Windows Server 2003 are available on the Internet. Try to download and install Windows XP drivers on Windows Server 2003 instead. It would probably work as both Microsoft Windows operating systems have the same architecture. Nothing can be said with surety though.
Go through the link given below to download the drivers for Windows XP.http://downloads.dell.com/Pages/Drivers/optiplex-gx520.html#Network
Hope this helps.