The camera hardware has a lot to do with it. Fast autofocus is a must.

Also the more open your lens (F-stop wise) the faster you can focus.

If your using manual focus the cars are so fast that its would be near impossible to get a good shot unless you get you fixed focus point down and have an insance shutter speed.

http://www.flickr.com/photos/philip-ester/470306734/in/set-72157600115652197/

I didn't do (try really) any of thos blurr speed pix due to my cameras slow autofocus. I will pick up a D200 to replace my outdated D70 before the nex ALMS.