The 3-in-one comprises of one of each of the following connectors:
Magsafe - to Power/Charge your MB.
USB - runs the built-in USB hub. Also, I think it carries the Audio and iSight signals.
Mini DisplayPort - Connects to compatible Apple gear to drive the display.
So the 24" Apple Cinema Display is only compatible with Apple Products including but not limited to your UniBody MacBook.