http://www.nvidia.com/object/notebook-win7-winvista-64bit-275.50-beta-driver.html
I also had this problem.. Nvidia sent this driver to use... after installing it, go into the Nvidia program and set it to default under the global settings. To be doubly sure that it is the card you're using... right click on the shortcut and choose it from the "run with graphics processor" Worked the first time for me. Good luck!