"Print Screen in Windows - F14
If you don't have the F14 key, press FN+Shift+F11"
http://forums.macrumors.com/showthread.php?t=611125
http://guides.macrumors.com/Taking_Screenshots_in_Mac_OS_X
http://howto.cnet.com/8301-11310_39-57436527-285/three-ways-to-take-a-screenshot-on-a-mac/
http://www.wikihow.com/Take-a-Screenshot-in-Mac-OS-X
Not sure if this works IN TA:K. If it doesn't, take fraps to take screenshots of the game... =P