Yes, if low light, go with the Nikon. Otherwise you will be spending money on fast canon glass, which won't be cheap with image stabilization. The Nikon body will give you a bit better noise performance at higher ISO's.
Still prefer Canon however. I have the XSi with the kit lens. I manage with the low light shots, but do feel limited. Editing on the PC sure helps.
IMO, the 18-55 won't be enough for sports (zoom wise, and speed to a lesser degree). A 200mm zoom would be a good start.
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