Since I don't have a Nvidia Card but do have have a Eyefinity Setup, I might be posting some ATI related stuff....but anyway.
Is your settings currently at Extend or Duplicate? If you hold 'Start' Key and then press 'p', it should display a mix of settings. When in 'Extend' it should just be like 3 different screens where you can maximise one program per screen. In 'Duplicate' the 3 screens should appear as one whole screen where any program maximised will take up all 3 screens.
In gaming, you can either run in 'Extend' where the game will take up the centre monitor or 'Duplicate' where the game will run with all 3 monitors. There are other options when you press 'start' and 'p' such as 'Computer only' and 'Projector only'.