here are some good and bad things about the d40 and rebel xt, xti
Good things about the d40 are:
1/500 second flash sync (the fastest shutter speed you can use with flash)
its lite (17oz)
Bad things:
no ISO 100
only 2.5 fps
Good things about rebel xt, xti
8mp (xt) | 10.1mp (xti)
ISO 100
3.0 fps
Bad things:
1/200 flash sync
1.8" lcd on xt
heavier (18oz xti | 17.1oz xt)
So really, it all depends on what type of photography your going to be doing. If you need a fast flash sync, go with Nikon. If you need ISO 100, then go with Canon. I have a Nikon and I love it, but im not going to say they are the best. In my opinion both Nikon and Canon both have there strong points. Go to a store and test them out, this way you know what your getting before you buy.
thats all