This is the most asked and unanswerable question on the web. It's like asking "how do I convert my CD's into player piano rolls ?".
The full answer is this: you cannot convert standard wave file of multipart music (normal pop music) into MIDI at all. It's too complex. Normally, MIDi files are created by keyboardists. If the music/WAVE file is monophonic, or one instrument only, there are several freeware programs that convert the file directly into MIDI (also some keyboards).