Likely the specific network adapter software device driver is not installed... WINXP installs generic drivers when and where it can ... and sometimes they do not work... You need to go to the computer manufacturer’s website and download (using another computer) the specific device drivers for the brand and model of the computer in question. Then install them - use a flash drive to transport the device driver files to the affected computer... Example Dell, HP/Compaq and others are quite easy to use...
LOL. Yesterday, one of my Vista boxes gave me a message that it had detected some new unidentified hardware (I've not installed anything new on it). It then said it had successfully installed the necessary drivers.
There must be a database of drivers for unknown hardware somewhere.
Weird.