If you're after a 2nd hand camera then there is always a good selection available in the Classifieds section; just be sure to exercise due caution when buying second hand gear from people you don't know (or even people you know for that matter!)
Also, what's your budget? I can't imagine a 2nd hand D40 is very much but then that's also a very limited camera, and I would expect that without spending too much more you might be able to extend to something like a D70.
READ MORE (read up more on the terms and understand them better first, and you can always do some homework on which is better for you)
SHOOT more (when u get your gear... keep practising)
Post more (to get feedback)