I think your comparing apples to oranges here. IK is like a tool/editor, and keyframes are like a saved file format. You wouldn't convert MS Paint to a .bmp, you would use MS Paint to make a .bmp. Likewise, you would setup your IK in 3D Studio to allow you to easily (and realisticly) manipulate your model. Then as you animate the model, you set keyframes along the way. Then you've arrived at your destination, keyframes.