Capturing the game screen

I am trying to figure out a way to capture the players' game screen for my dissertation. The traditional method is to have them play the game and locate a video camera over their shoulders. However, this is not the most ideal, since the presence of the camera might affect their playing and the quality of the screen recording will not be as high.

I came across with an article on a usability testing program called VULab. It looks very neat, where you create a pre test, allow people to play with a website and give them a post-test. Unfortunately, when I have created a demo experiment, it did not save the screen for me :(

A friend of mine recommended me Adobe Captivate 4. Just like creating a demo, I can make the gamers record their game with that program.

Still searching for the best way to capture their game screens...