If you're looking digital (DSLR) stick with Canon or Nikon. As to which brand to choose.......it's truly personal preference.....and a much, larger issue than we should even start here. I've only had experience with Canon and love them........
As to what gear to get......DSLR....the Digital Rebel XT isn't a bad camera for the money but as others have already stated the 20D is a great camera as well. I instead would steer you in another direction.......check out used Canon 1D cameras for their superior autofocus and weather sealing abilities (when used with their "L" series lenses, Canon 1 series cameras have phenemeonal weather sealing.
If you're not made of money don't go Digital......the cost of CF (compact flash cards, DSLR body, lenses, flashes, photo editing software, etc) will make you cry.....
instead check out a used Canon EOS 3 film camera. It offers all the performance of their 1 series cameras and are available for $300.00 without the power booster (ups the FPS advance of the camera to an impressive film shredding abilities and adds vertical shutter release).....and check out some third party lens from Sigma.....
The cost of an EOS 3 used with a fast telephoto zoom and wide angle would be under what the body of a 20d would run you......pick up ADOBE photoshop elements and have your local lab just brun your prints to cd...you can edit them later. These would be a great way to get into taking qaulity action shots.
Remember it's not just the gear..
Chris