Congrats on the new gear. I'd love to get the 100-400 someday. Does it work with a teleconverter? I definitely think you should keep the 40D as a second body for Yellowstone. Not only do you have the gas and water vapor but dust and dirt. I'd hate to be changing lens often in that...
Man, I had no idea this thread had grown so much. First, congrats, Ron. Even though it's a Nikon it's still a DSLR and will be a lot of fun to use. I saw mention of bags up-thread. Depending on what style you're looking for the new Think Tank Retrospective series is getting rave...
I'll third the recommendation for B+H Photo. I buy most of my gear from them. Make sure you check out the shutter lag numbers on any P+S you're looking at. I suspect anything in the price range you're considering will be very good. As others have said, don't get sucked into the MP race...
Ron, I think most of what you need to know has already been covered. If you're going to treat a dSLR like a point and shoot then it's better to get a point and shoot. Something that can fit in your pocket and is with you all the time is much better than having a dSLR that you decide to...