Something like the 7D or eq from the other brands should make be able to track a grey hound easily enough, just need a lens that has a fast focus system. Then a 70-300 lenses might be enough. Also having the aperture of 5.6 at 300 will give you a bit of subject isolation to make the dog stand out a bit.
just thought id update everyone.
i threw the hs10 in the local tip
Purchased a Nikon d7000 with the 18-105 kit lens
a flash and some wireless triggers
a nikkor 50mm f1.8d
and a manfrotto ballhead tripod
and the results are great
i use the body with the 50 1.8 at 2.8 320th sec and the flash at 128th power and im really happy with the shots and the focus.
thanks guys just thought id give an update