As to the D90 vs. D40
First, definitely get them in your hands. I bought a D200 sight unseen a while back, and it did not fit with me at all. Even my big bass player hands didn't like it, so out it went.
I started on a D40, and gradually became dissatisfied with a few things about it. One was that it couldn't bracket exposures, and I like to shoot HDR often, and the other was that it was hard to get a good feel for white balance off the screen. The D90 brackets three exposures, which is better than none and worse than 7, and the screen is very nice, if not terrifically more helpful.
I got the 90 because the 40 didn't do what I wanted. If the 40 bracketed exposures, however, I'd probably still shoot it over the 90 and spend the extra money on lenses.