Help and Tips on my photography?

I've had a camera for a while and only recently have started to use it. I've noticed the still shots usually turn out better. 90% of the time when I take a picture of a moving thing (usually horses) they come out blurry somewhere. I own a Nikon D90, and usually have the camera mode on non-flash, is there something else I can be using when taking pictures of faster subjects? I know about aperture and all that stuff, not in too much detail but I do know how to change it. Can I go into manual mode and get a setting that is good for this? Also any tips of taking photos or how to improve on mine I will appreciate.

http://naturalhorses.deviantart.com/gallery/ - If you look at the Chestnut Gelding stock and both of the Herd stock images you will see what I mean.

Simple，Use a High shutter speeds & a larger aperture
High shutter speeds enable moving objects to be clearly photographed.

Go to betterphoto.com, popphoto.com and submit some in wantimages.com

Http://naturalhorses.deviantart.com/gallery/

Its all about the shutter speed and that depends on the aperture and ISO being used. I suggest shooting in Shutter Priority at ISO 400. Set your shutter speed to 1/500 sec. And as long as you're outdoors your camera shouldn't have any trouble selecting an aperture that will give you a good exposure. At 1/500 sec. Any motion blur should be eliminated.