I recently wanted to capture the images on my screen for a slideshow presentation. I had to be booted into Windows to demonstrate the actions, but I was on a MacBook Pro. MacBook Pros do not have a Print Screen button, nor does the Apple command, Apple+Shift+3 (or 4) work. What to do? Use the On-Screen Keyboard that comes with your Windows system. It has a print screen button and it works! I pasted my images from the clipboard into the GIMP and it worked out great. I will walk you through the steps to get to the On-Screen keyboard. I would like to thank the author Half-Brain in this forum for coming up with his solution: http://forums.macrumors.com/showthread.php?t=236049
3. Go to Accessories
4. Go to Acessibility
5. Click on On-Screen Keyboard
Now you have the Print Screen key to use.