You mean write Sheet music and create midi from it?
I'm sure there are a few good free ware midi-creation program out there .. I think i had one at some point
If I find one I'll let you know. (You could always use Linux, I'm sure there's a similar open source tool :P)
EDIT: think I found what you need
http://www.anvilstudio.com/ -- with the free version you can make as many midi files you want .. the non-free version also lets you mix audio clips, so you'll be fine with the free version