All the DSLR's are good. You really can't go wrong with any of them. I chose the Olympus system due to the weather sealing(of both the E-1 body and lenses) plus the dust shaker on the sensor. Since I am in barns and outside in all weather, it is what put me over the edge for the system.
Canon users will say the Canon is better and Nikon user's will say the Nikon is better. If I were to change to a different system tomorrow, it would probably be to the Nikon D200. I personally like the out of camera color of the Nikons. I think they do less smoothing (noise reduction)
If you want to shoot high ISO often, no one beats canon. Though the Nikon D50 comes close. Canon is the high ISO leader for sure
I would go to the store and handle the D70 and Rebel XT. I personally like the feel of the D70 much better. I prefer the menus and it has a few more options the Rebel doesn't
Both are very good cameras and again, the ending image quality is going to be a mixture of what lens is used and your photoshop skills. DSLR's do much less in camera processing.