Open Device manager, under Network adapter find which LAN chip is on the MB, Marvell for esample. Go to the LAN distributor's online download page and download the latest driver. Hint. Vista drivers work for Win 7.
Have you gone to the manufacturers website to verify that a driver for that particular hardware exists for Windows 7? Also, have you verified with Microsoft Windows 7 Compatibility Center that the software is indeed compatible with Windows 7? The Microsoft Windows 7 Compatibility Center is available here: http://bit.ly/1gW6Ns and can be used for both hardware and software concerns.
Should you require additional assistance and guidance, Microsoft does have an official Windows 7 Support Forum located here http://tinyurl.com/9fhdl5 . It is supported by product specialists as well as engineers and support teams.