This is the case: You have a MacBook or a MacBook Pro (I supose it should work on a iMac too), and for some reason you have Windows(r) installed and want to take a screenshot (printscreen).
This was tested with BootCamp 2.0
Since the MacBook/MacBook Pro don't have a "printscreen" key you shoul try this:Shift + Fn + F11 (If your functions key controls the hardware)
Shift + F11 (If your function keys bahaves as normal functions keys)
If you want take a screenshot of the active window jus add the Alt key.
Alt + Shift + Fn + F11 (If your functions key controls the hardware)
Alt + Shift + F11 (If your function keys bahaves as normal functions keys)