I've succesfully used a 70-200 f4 outdoors and a 100mm f2 indoors
later I bought a 70-200 f2.8 IS and that one gave me more good shots, not better shots. Indoors I still prefer my 100mm.
DON'T buy a 5D Canon for (indoor) RC (have read it above somewhere) the focus points are crap, only the middle point is 'ok'.
I would recommend lenses faster than f2.8 as that activated cross type AF sensors and gives you AF on horizontal and vertical contrast.
85mm or 100mm indoors and get yourself close to the action will give you nice shots! (and it's cheaper)
Go high in ISO if you need to, better to have a noisy pic than a blurry one.
resize, sharpen!
It still is 40% material and 60% technique. If you don't know how to use your camera outside auto modes or can't follow the race with a smooth hand, your shots will be crap, even if you've got good equipment.
Give me light, a cheap camera and I'll give you great action pics, but it won't be 500 good ones. Like my 1D would ;-)
Good luck
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