I'm a software developer. If the game does Direct3D calls directly, then it's a matter of setting refreshrate to the monitor's refreshrate (can be enumerated with DXGI) and setting fullscreen to true. (Or windowed to false if Direct3D9).
There might be problems on a multi-monitor setup though, so that requires extra fiddling with the window.
Doing windowed fullscreen is easier to deal with for the developer than exclusive fullscreen, but it may reduce the performance of the game. Besides the obvious fact that you can't have a different resolution than your desktop.