Ok.... how much does such a keyboard cost? Can you recommend me one?
Well like Olimar's saying, you may want to try other methods before going MIDI. Keyboards can range in price from $80 to $300 (if you get all the useless goodies). If you go for it though, you have to be sure it has MIDI capabilities. Look for a MIDI Out line coming out the back. Ask lots of questions. Nothing's worse than taking something home and finding that it's not what you were looking for or doesn't work.
But if you go so far as to get a keyboard, I'd recommend one that has built-in speakers. Otherwise it's useless unless plugged into a computer. Which is really stupid. As for brands, try Yamaha. They're pretty solid. I've also heard good things about Casio. So they might be an option too. But stay away from M-Audio. That was my first keyboard which I never got to work and they never have built-in speakers. What I use currently is a
Radio Shack Concertmate 990. It's a really nice keyboard. I can definitely recommend Radio Shack. (Last I remember hearing about the exact model, it's no longer in circulation. Although I'm not 100% sure about that so don't quote me on it)
One more thing on getting a MIDI keyboard is ask about the need for an interface. A new one usually ranges quite drastically in price, the cheapest I've seen being about $110. Of course, an acquaintance of mine found one at a pawn shop for $20. Try Ebay or something. But ask lots of questions about it because you may or may not need it. I'm a little fuzzy on all the details myself..