Hello Sarah,
I would echo those above and say that the 400D is a very good first DSLR. I bought one a few months ago and am very happy with it (although I still have a huge amount to learn!).
You don't say what it is in particular that you want to photograph but if you are interested in bugs and flowers, as I am, you will want to get a decent macro lense.
Good luck and best wishes.
