Hi I'm new to photography and hense new to the forum.

I recently had the idea that I'd like to try my hand in sports photography and obviously need to get a camera before going to college or anything.

I was looking at 3 models, Nikon D5000 and D90, and the Canon 450D. Does anyone have any opinions on these models and/or suggestions for what else to look at?
I'd rather the price range be 500-600 however will stretch it if needed.

The sports I'd mostly be shooting would be Karting/motorsports, and some extreme sports like skateboarding n rollerblading.

Any help is appreciated.