If you look at your keyboard and see a command button, then yeah, Limey's way will work. More specifically if you have a Mac, here are all the keyboard screengrab commands:
Cmd+Shift+3 = Save file to desktop containing screenshot of full screen
Cmd+Shift+4 = Use a crosshair to grab a section of screen, save selection as file to desktop
Cmd+Option+Shift+3 = Copy image of full screen to clipboard
Cmd+Option+Shift+4 = Use a crosshair to grab a section of screen, copy selection to clipboard