Just throwing my two cents there:
1) The 40D has a two-step shutter button. Make sure you are focused and focused on the correct place before you press the button all the way. Normally the 40D will focus on the closest object it finds in its focusing spots, so beware: if you are shooting through glass or something, it might focus on a smudge on the glass, or the wrong player.
2) If you are using the kit lens, you HAVE TO turn image-stabilization off for action shots, or it will introduce unwanted movement into your shot.
3) Try not moving your camera too much during shots. It's just a camera like any other - if you move it, it will blur shots.
4) If you try to pan a moving object, make sure you are doing it right (I know I am not, that kind of thing takes practise and lots of ruined shots).
5) Use a telephoto lens with 2.8 apperture. Your kit lens is way too slow for this kind of work. The lens suggested above is great. It's an expensive monster, but it's an expensive monster that will do the job for you. Make sure you turn off horizontal IS for panning.
6) If you like put your camera in manual mode and set it so that your depth of field is the entire court, or that part of it that you are interested in. This way you don't have to waste time and worry about focusing. You can also combine that with panning and get a really nice blurring effect.
Something else? You really aren't giving too much detail.