When you are shooting sports photos, the normal mode for the Canon 350D is pretty useless. It is by default set to according to the "tutorial":http://creativekarma.com/ee.php/weblog/comments/exposure_modes_on_the_rebel_xt/
1. Program. which means it chooses the aperture and speed automatically. This is usually too slow for sports where you want it to be 1/500 second or faster to capture the action
2. Focus. Usually set to AI Focus which means it guesses and tries to figure out which one of the 9 cross hairs the object lives in
3. Exposure. Normally set to evaluative metering (the first selection).
4. AF sensors. Normally all 9 are turned on
The problem is that you don't want any of these for sports where you just want to take a photo and have it sharp on what you are pointed at in the center, so you have to change all three modes:
1. Tv mode. Which means allow the aperture to vary and then set the exposure time. In bright sunlight, I normally set it at 1/500 sec. You need a fast lense or a high ISO to make this work. With a 100-400 lense that is pretty slow, it means lots of light shooting at ISO 400.
2. AF Sensors. Just make it the single sensor in the middle. You do this by holding the AF sensor button and moving the thumbwheel until you get one cross hair
3. Center-weight average (this is the last of the three modes and looks just like a squarish box) because with evaluative, if you only have one sensor on, it just uses this and you get bad exposures.
4. Focus. Pick AI Servo which when you partially press the shutter will keep the camera focused on the center AF.