Have you verified that your graphics card is indeed compatible with Windows 7? You can easily verify compatibility for both hardware and software directly with Microsoft at the Microsoft Windows 7 Compatibility Center available at the following link: http://www.microsoft.com/windows/compatibility/windows-7/en-us/default.aspx
Also, have you ensured that all of your drivers are up to date?
Should you require additional assistance and guidance, Microsoft does have an official Windows 7 Support Forum located here http://social.technet.microsoft.com/Forums/en-US/category/w7itpro/
. It is supported by product specialists as well as engineers and support teams.
Microsoft Windows Client Team