Multiple exposures are possible using a DSLR whether in photoshop or DSLR itself.
Here is one I did some months ago where the object was to use flash to detail the camera but this would show the screen black even though on so multiple exposure was used in camera to have a second ambient light showing monitor only then combining the two.
Multiple exposure feature is available in a Nikon D2X but not on the very similar D2Hs so not all cameras have this feature.
http://www.worldphotographyforum.com...500&ppuser=101
I am planning another and when complete will post.