Mouse rotation?

Get the difference between last frame''s mouse position and this frame''s mouse position, the bigger the difference, the bigger the angle of rotation should be. Experiment with different degrees for the rotation, until you get the effect you want.

Also, consider limiting the maximum degrees of the rotation, so you can maintain a believable speed of rotation.

use directinput for mouse rotations. the GetState function writes to the DIMOUSESTATE structure which contains the x and y values how strong you moved the mouse.