To everyone still having a problem with Print Screen, and none of the proposed solutions work: I have your answer!
I recently bought a brand new laptop, and I'm running both Ubuntu 10.04 and Windows 7. I'm a Simmer, and I was getting more and more frustrated that I could not capture the screen on my Sims game so I can share my CC. Nothing anyone on here said worked, and then I found this.
It worked for me, and I hope it works for you all!
Close out of the program you are having trouble with capturing the screen.
Right click on the shortcut of the program on your desktop (in my case it's Sims 2 Apartment Life).
Click on Properties .
Click on the Compatibility tab.
In the middle area of that tab, there should be a bunch of check boxes under Settings. Click in the box alongsideDisable desktop composition.
Apply the changes, click OK.
Open up you program, press on your Print Screen (Prt Sc) button, open up a paint program, paste your image (Ctrl + C) and voilà! It should work! ^_____^