I have a Raspberry Pi Model B and the display unit from a Dell laptop - functional, but removed from the laptop because of a broken hinge. Is there any way the Pi's GPIO pins can be used to drive the display unit directly, to function as the Pi's monitor?
It might be possible, but
Such displays often use a parallel interface (4, 8 or more data lines, lots of control lines) and the Pi has only a few GPIO available on the extension connector. (You can guess the number of GPIO simply by counting the wires in your interface - likely a flex cable).
I don't think anyone has done this yet, it will not be easy, and there is not much incentive to do this for any particular screen.
So unless you are in it for the thrill (and willing to spend a lot of time on it) I would say: forget it.
The display almost certainly wants data at a significantly higher frequency than you can output from the Pi. If it uses a standard LVDS interface then you may be able to find a cheap aftermarket controller for it that takes video inputs (this is commonly done by people making DIY projectors out of laptop display panels) and connect that to the Pi.
The rasberry pi has a yet-unused lcd connector which would be worth investigating, though an adapter (more than just cabling) and detailed register programming data may be required.