Go into Control Panel>System>Hardware>Device Manager, find the ethernet adapter under eth heading of Network Adapters then right click it and go to Properties.
Click the Details tab, then scroll to Hardware IDs and note down the four characters after VEN for Vendor and the four which follow DEV for Device. Go to http://www.pcidatabase.com and input those details in the relevant boxes and you will see the list of all the right manufacturer's products but sadly, they aren't in order. Use Internet Explorers Edit menu then Find to type in the DEVice ID and the search will find the correct entry. Follow the link to the site for the correct driver and download it. That site should be the manufacturer (OEM) own website which is always the safest place to go for drivers.
If you need more drivers after that, you should by then be connected to the Internet so the system can search for them when you click on Update Driver in each device's properties page.