Why does the Windows Vista Control Panel report that my GeForce graphics card has less memory than it really does?
This is due to a limitation in the algorithm that Vista uses to calculate and display the amount of dedicated graphics memory on a graphics card. This is a Vista reporting issue only--the graphics card and driver are still able to access and utilize all of the video memory present. Note that the NVIDIA Control Panel reports the correct amount of graphics memory.
For more information, please see http://support.microsoft.com/default.aspx?scid=kb;en-us;936484