No, there is no software for converting WAV audio to Midi - they are completely differnt things (like converting a vehicle into a television). Midi stands for Musical Instrument Digital Interface is is really just a standard for recording the length, pitch and velocity of notes, usually played on some kind of Midi compatable instrument. The computer then interprets this data and matches the note information with prerecorded sounds (usually stored in your sound card).
WAV data, on the other hand, actually records the sound of an instrument (or whatever).
There are plenty of tools out there for creating Midi music. At the moment I use Cubasis AV which I got free of some magazine. Cubasis lets you create music by editing music scores (like Finale, mentioned by gofamon), with a keyboard (or other Midi instrument) or by way of drawing notes onto an on-screen keyboard.
Phew! 🙂