The Nikon D40x has been introduced just after the Nikon D40, integrating a sensor similar to the one used in the D200/D80 cameras. The sensor is the major difference between the D40 and D40x. Thanks to that sensor, they have been able to increase the fps from 2.5 to 3. The form factor is the same.
The D40x is a 10 MP camera and has been replaced by the newer D60.