Internet help

Go to the manufacturer's website and find your PC. From there find the drivers for the ethernet card. Sometimes called the NIC or Network Adapter. Download them and install them.
You can see if they're installed or not first by opening the device manager (right-click on the "My Computer" icon, select "System Properties," go to hardware -> Device Manager) and seeing if it appears in the "Network Adapters" list.

If it doesn't appear, has a yellow exclamation mark on it, or has a red x, you'll need to install the drivers.
The only reason i think the drivers are not installed is because that is the major reason why most XP installs cant access the internet. Even my XP install cant access the net till i install my ethernet drivers.
You're most likely right, I'm just providing the information one would need to fuly understand the situation they're in.