That's a decent amount of money to spend on buying into a dSLR, but on that budget you're likely still better off saving money on the body to spend on lenses. That way, its easy to upgrade the body later on when your needs increase, but you keep all the same lenses.
With the new Canon Digital Rebel XTi, the Rebel XT will likely come down in price. Already you can buy that for around 6-700 with the kit lens (f/3.5-5.6 17-55mm) perhaps cheaper now that the XTi is out. That should take some decent night pictures, and its fairly wide angle.
For sports, look for a second hand Canon 70-200 f/4L telephoto lens. If you're shooting in bright sun most of the time, the f/4 won't be a limitation, and it is a fantastic lens, and is my primary sports workhorse. All the shots in my sig were taken using that lens, some coupled with the Canon 1.4x teleconverter. Secondhand, the 70-200mm f/4L will probably run you around $500.