If, in fact, the center focus area can be locked, then my hopes for buying the D40 are renewed. I guess I need to download the D40 manual for a read.I almost always use the centre focus area whatever camera I am using, and my only wish for this camera is that the central area could be locked, which it cannot be. Instead the focus area can be moved using the paddle at the rear of the camera.
You can choose which AF area is being used, but I don't believe that you can lock it down.
You do know which focus area is being used though, because the focus area bracket outline is illuminated as you choose it with the "paddle" and when you half-press the shutter release.