Dust keeps showing up

I have a Nikon D5000 with a 55-200mm lens that I'm taking pictures with for dirt track car races but i keep getting dust spots in my pictures. I use a Nikon Speedlight SB-600 flash so what can i do to keep the dust down? Should I use a lens hood?

Get a longer lens and stand further away ;-)

A lens hood will reduce the angle of attack for dust but won't stop it all. Put a UV filter on the lens for protection and carry a lens pen to regularly clean away the dust.

I've been to dirt track races. That dust gets everywhere, in your ears, eyes, nose. Your coat and hair are covered with a fine powder of dust by the end of the night. I'm afraid dust is just the nature of the beast where you are shooting. There's no magic dust repellant. You just have to clean your equipment more often. A plastic bag rain cover may help, like these:
http://www.bhphotovideo.com/...4137411777

Install a UV filter on the lens then arm yourself with a pad of lens paper.

Sounds like dust on the sensor not on the outside of the lens. It has to be almost mud before dust on your lens or filter will show up in photos. If the spots don't move from photo to photo its on the sensor.