I think the choice of Canon vs. Nikon is entirely personal, I know professional press photographers that use both, and some switch from one to the other more often than I care to think about.
As for lenses, I would recommend a a long focal length 200 or 300mm. Some sort of vibration reduction might be useful to allow handheld shots at lower shutter speeds (although you will probably want faster shutter speeds to freeze the action anyway).
For this sort of money, new at least, I personally would recommend a Nikon D40. The camera was only out for about 9 months before it was replaced with the D40x and is now available at great prices.
Here it is on ebay having sold "Buy it now" for £308 with the stock 18-55mm lens and a 55-200mm lens.
I think this would be a great starter kit.
A couple of good places to look are:
www.kenrockwell.com (difficult to navigate, but some good product reviews)
www.dpreview.com (product reviews dating back to some quite old gear if you are looking at second hand).