Welcome to Seven Forums.
When you installed, did you allow 7 to check for updates over the internet? I haven't had any problems with any of the 7 builds, but I have had to install nVidia's drivers rather than windows drivers to get everything working correctly prior to the RC. I haven't had any problems yet with the windows WDDM driver in RC7100 or in 7201.
Have you tried windows update to see if there is a driver update for your card.
Hope this helps.