See the next thread down regarding VST and converting audio to midi.
Really it all depends on what you expect to achieve, and how must supporting work you're prepared to do.
It may well be technically 'possible', but it may not be 'practical'!
Follow the link to the Widi system, the link hidden behind a one word reply (the word 'here' is in fact the link), this system maybe CAN do what you want, but you'd need to work hard for it. Also, my reply further down refers to the Roland CP-40 (?) unit which CAN accept a microphone and does produce midi, but again, the result needs a fair bit of further. work. I'm happy to discuss what you're after in more detail.
Geoff