You really have no reference points? (And no lenses?) I would think that even if you're switching from Canon or Pentax or something you would have some notion of which lenses you used to use.
If this really is your first DSLR and you really don't have any lenses or any experience with lenses, I'd start with the kit lens, the 24-85 AFS VR. It does a good job with landscapes, general family stuff, etc. While I shoot a lot of motorsports, I've never been to the Melbourne event. But I'd guess that you'll want at least a 70-300 AFS VR if not something longer - probably something like a Sigma 150-500 HSM OS or 50-500 HSM OS. In your position I'd rent for this purpose as this is a $1000-$2000 investment and it doesn't seem that you're so focused on this sort of photography that it would warrant a permanent investment.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!