[Mau5]

Haha here are examples of the free ones.
MuseScore: http://www.youtube.com/watch?v=OJWiv6zn0Ig
Csound: http://www.youtube.com/watch?v=KxyBTr0eamQ
BuzzMachines: http://www.youtube.com/watch?v=TcqH9591gDM

You can go out and buy something like a USB piano keyboard and/or controller and it is so much easier, it is almost essential. If you have the cash i HIGHLY recommend it. I use the Akai MPK25, it's relatively cheap compared to what other equipment is worth and it's really everything i need. Equalizer, recorder, MPC, and 25 keys. That being said you can go out and buy a simple USB piano keyboard for anywhere from 60 to 120 dollars if you're looking for something cheaper.

Here is what i use. http://shopping.yahoo.com/848186598-...trio-software/

Edit: If you have the money, or will have the money someday, i'd buy Ableton Live. It's the best music writing program i've seen to date. Everything you'll ever need to make music is included.