If all you have is a 14MP camera, you need to shoot many small sections of the original and merge.. but you know that.
What you need to do is build a movable wall that the art is set up on and that way you move the WALL and not the camera.
The camera and the lights stay in the same place and then each section is shot.
Plan to shoot the highest section first, then lower the tripod for the next layer and so on. You do need to make sure the lighting is equal as possible over the entire piece.
The other way to do all this is to get the 4x5 and a Betterlight system. Larger areas of the art captured at one time and huge, high resolution files.
Go to the Betterlight site and check it out.http://i65.photobucket.com/albums/h216/framah/_98X4005smallcopy.jpg[/img]]