Dell optiplex gx280 drivers free download xp
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On the case of your computer, Dell has put a printed label with eth Service Tag reference.
If you go to http://www.dell.com and click on For Home and then on Support and Services and input that reference, all the drivers for the specific hardware they installed in your system will be available. They will be executable files so when you've downloaded the ethernet adapter driver, double clicking on it will be enough to trigger the installation process.