Do I have a Powerbook or a MacBook?
The name of all of Apple's notebooks is clearly stated on the frame of the screen on the bottom.
The System Profiler application in the Applications -> Utilities folder on Mac OS X, or the System folder -> Apple menu items folder in Mac OS 9 has a Machine ID, which can more closely identify the machine, and that would appear as Powermac x,y or MacBook Pro x,y
where x and y are numbers. These values are essential to identify what features the computer may have and its compatibility.