Kbase Article of the Week: Cannot Select GeForce 9400M Graphics in Windows on MacBook Pro (15-inch, Late 2008), MacBook Pro (17-inch, Early 2009), MacBook Pro (15-inch, Mid 2009), and MacBook Pro (17-inch, Mid 2009) »

Long title; short article:

You may notice that the built-in NVIDIA GeForce 9400M graphics subsystem does not appear in the Device Manager and cannot be used with Microsoft Windows XP or Vista.

Windows is not able to take advantage of the GeForce 9400M graphics processor and by default uses the GeForce 9600M GT discrete graphics processor.