Windows print screen when using Boot Camp
Follow these instructions in order to map the F13-F15 keys on an Apple keyboard to the functions, Print Screen, Scroll Lock, and Break commonly found on PC keyboards:


On your PC, copy the following lines into a text file.


REGEDIT4
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layout]
"Scancode Map"=hex:00,00,00,00,00,00,00,00,04,00,00,00,46,E0,5F,00,46,00,5E,00,37,E0,5D,00,00,00,00,00


Rename the text file remap.reg
Double click on the file remap.reg and answer yes to the question about adding the information to the registry
Reboot


Function keys are now remapped to their PC equivalents

Source: MacWindows.com