Your lense for action shots and wildlife will cost a pretty penny. For Nikon, get the D50 or D70s and get a fast telephoto for your action shots and wildlife. Ditto for Canon, the Rebel XT will be a good enough camera. Where in Texas are you? If you are in the DFW area, you can check out my D50 and lense set-up (a 18-70mm zoom and the awesome 70-200mm VR lense). In cameras, you get what you pay for. Spend more on your glass and the cheaper bodies will be good enough. I don't think you need the more expensive bodies. It is analogous to scopes. The better scopes certainly look better, but cost more. Better lenses will be more expensive, last longer, and get better pictures.
Edit: I wouldn't get the D100. It is an outdated camera with old technology. The D70s is a much better camera.
Note: There are two versions of the D70, the D70 and the improved D70s. Try to get the "s" version if possible. USB 2.0 transfer, larger screen, and other minor improvments.