I'm sure this will work with Win 3.1, I just haven't had a chance to run through an install procedure yet. There are plenty of machines at work with Win 3.1 and I should get a chance this week to sort something out.
a) Sorry, I've never had a chance to use a Mac. Are there any Mac C programmers listening? If so you are welcome to my code.
b) There is at least one program (Autoscore) which converts pitch to MIDI fairly successfully. A mate of mine has it but doesn't seem to have used it much. I think there is another program which converts wav to pitch with moderate success. I wouldn't be too hopeful but maybe the two programs could be made to work together.