Do you need SLR or point and shoot? Digital or Film?
If you are serious about this. The first thing that you need to do is really look at what sports you would be photgraphing, under what conditions, etc.
Once this is done then you can look at determine things like the focal lengths you will need, fps, shutter speed, high speed flash synch, etc.
The determination of the focal length will let you decide which lenses you want and hence which manufacturer you want to go for. For example if you have to have IS then Canon is far beyond Nikon at this point. If you want very good used lenses then go for the Nikon.
Now that you have decided on the manufacturer you can determine the body that you will need. If you want a amateur cam then the D70, or D20 might be the way to go. If you have the money D2X or the Mark2. That's if you want digital, me if I were starting out I would stick with film and would go for something like a second hand F100/F5 or EOS1.
All of this is if you are serious about this. Otherwise any camera will do and it is your vision, in the sense of timing, framing and composition, that is more important.
I know a lot of people will suggest digital point and shoots, but if you are going to take this seriously, you need something slightly more involved.
Hope that helps some.
Rav.
P.S. Don't count film out it has a lot to offer.