It does sound as there may be a driver compatibility issue that may be causing the graphical issues you experience. What is your graphics card and what drivers are you using with Windows 7 RC?
Also Windows 7 will be officially released later this month. One of the most significant improvements in the final version of Win 7 is found in the area of driver support. In the meantime, Microsoft does have an official Windows 7 RC Support Forum located here Windows 7 Category
. It is supported by product specialists as well as engineers and support teams. You may want to also check the threads available there for additional assistance and feedback.
Microsoft Windows Client Team