Then if you don't have the motherboard driver disk, what you have to do is open up the case, and find out the make and model of the motherboard, then once having done that, go online, (with another computer), to the motherboard manufacturers website, and download the drivers for that type of motherboard. Once having done that, burn them onto a disk, and use that disk to install them on your problem machine.
NOTE : It could be that you are missing the motherboard's "Network Adapter" Driver, and that is preventing you from going online. Though, as I said before, once you have your "Drivers" installed, DISCONNECT your internet cable, and install Windows XP Service Pack 3. Once that is done, reboot once, then shut down and reconnect your internet cable, then try it to see if it works properly, - i.e. updating Windopes.