Yeah I've heard of this being possible, yet midi is recorded in a different way than MP3. I find it rather hard to believe you can.
MIDI works by recording seperate channels and the files contains information regarding to what bank to play (instrument) and what frequency of key to use, which is processed by your sound card software.
The thing is, MP3 is a compressed WAV file in more respects, and since it works in another way than MIDI, and doesn't contain just file data, and contains the full streamed sound, I find it hard to believe a program could listen to a MP3 file, and then hear frequencies and record them into MIDI format.
I'm not saying its not possible. I'm just saying it would be hard to. It would be possible though for example to make a MIDI a MP3 file by just recording it...
What I tihnk you should do since MIDI on different peoples PC's sound worse than each others, I would record a very low quality Wave file with a song on it. It doesn't even have to be in stereo, or have a high rate, and shouldn't take up that much space to send over the internet. Even better if it supports MP3, use that
Sorry I couldn't help you with a specific program, I honestly don't think its possible in the way your thinking.