Instructions
Navigate to the Fraps website and download the latest version of the application. The full version of the program has more advanced features, but to test the fps in games, the free version works perfectly.
Install the software on your computer after the download is complete and then run it.
Click the "FPS" button at the top of the program screen and change the "Overlay Hotkey" to something that is convenient for you. If you are satisfied with the default key (F12), leave everything as it is and minimize the application.
Start "BioShock" with Fraps still running in the background. Once the game has loaded and you are playing, press the key you have selected in Fraps to display the overlay. The fps will be displayed in the top left corner of your screen. By pressing the hotkey again, you can shift the fps display to any one of the other corners.