One lens to start out is a good idea, so you can just focus on using the camera. If it was me I would bring the 28-105, just for the versatility. I would guess you won't be able to get real close to the race, so a little extra zoom may be nice. A somewhat wide angle could get some good photos of the whole track as well. Not sure how lighting will be, but may have to shoot at higher ISO's to freeze the motion of the racers. I use a Nikon D80 and it allows a person to shoot RAW+jpeg, so you get two pictures at once. This may be handy, so if you have a tough time with the RAW conversions you still have jpeg's. Your camera should come with some kind of RAW converter, so you can try it out first and decide if you want to buy something different down the road.
Happy Downloads!
http://www.sprintingturtles.info