I have a 9000 pro 128. It tries to put a 19" image on the 15" screen. The Help file is not helpful. It only tells how to change a setting, it does not tell what any of the settings do or why you would want to change them.
I have the 19" at 1152 x 864 and the 15" at 1024 x 768. If I set them both the same, nothing changes.
Adjusting the screen size settings on the 15" only shrinks the display area, without fitting the entire image into the screen.
'Extend my desktop onto this screen' is checked for the 15". If I uncheck it, everything moves to the 19" and the 15" turns off.
I can't think of anything else, but I don't know anything about videocards either.