Another vote for the Nikon D40 or D40x. If you are looking for trackside action or sprts photography, start saving up. You will need the new Nikon D3 ($5000) or D300 ($1800 or so, can do 8 fps with battery grip), a fast (f2.8) lens like the famous 70-200 f2.8 zoom ($1600) or the 200 - 400 f4 zoom (another $5 or 6 grand). Both with VR (in-lens vibration reduction)
Seriously, the D40 or D40x should do fine, and you can always upgrade lenses when you can afford it. That's the beauty of dSLR's.
If the D40 has an optional battery grip. which will allow you to use two regular rechargables, or a set of AA's instead of the rechargables. I know my D80's battery grip has that option.