First off, you need to shoot in one of the creative modes so you can use center weighted average metering. Meter on the subject you are shooting, and you will get a much better exposure. If are you not comfortable with setting your own aperture and shutter, you can shoot in Av, (aperture priority), set the aperture to it's widest, and the camera will meter on the center portion of the frame, and set your shutter speed accordingly. You can use exposure compensation to bring it up a bit if it's still too dark.
Of course you'd be better off with a 20D, but if you could afford one, you'd have bought it straight out. The Rebel will serve you fine with the right lens and some know-how. I don't know how close you'll be to the action, but you might want to look into a telephoto lens for this stuff. Be prepared to spend some big bucks though. Depending on how close you can get, you might get away with an 85mm 1.8, or you might need to splurge and get the 70-200 2.8 IS.
About the error 99; Dirty lens contacts can cause that. Power down the camera, remove the batteries, and dettach the lens. Make sure the metal contacts on the lens are wiped clean before you attach your lens. Then put in the batteries and power it up. It should be ok. If not, it's possible that you have a factory defect. Send it back to Canon.