In the Motion Blur pop-up window, select the amount of blur distance that you see fit. In this case I selected 30 pixels. Make sure to adjust the angle of the motion blur to suit the direction of the subject in your image.
Now that your image has a good blur to it, select the History brush from the left toolbar, as shown below.
With the History brush, start 'painting' over the main subject, to get the blur effect off it. As you can probably notice, we didn't apply the History brush on the whole horse, instead we kept some parts like the back section of the horse and the hind legs in motion for a more natural effect.
And, with a little cropping we have this as our final image.
Good .. one .. nice that. tech2 has done this 
