Does the Nikon D40x support SDHC class 10 and 6 cards?
Do you know whats the list of supported cards by the D40x
According to DPreview it supports SD and SDHC cards. This includes all the classes of these cards.
The classes only differ from each other regarding write speeds. Here is more information on that.
As the D40x can not record video, a class 10 card is not necessary. A lower speed card is sufficient to take pictures.