if u have fruity loops u can open midi files into the program and then save as MP3.
otherwise try searching for MIDI to Wav converters. Once u have it in Wav format download Music Match n convert it to MP3.
But the thing about midi is that the output will only be as good as the sounds used to play the output. Unless u assign quality sounds to be used as the instruments, then when you convert the file it will use the General MIDI sounds stored on your Sound Card. 99% of the time these sounds will be crap. This is why most people have a low opinion of midi. Because most MIDI arrangments on the net are poorly done and when played using general MIDI sounds the music is similar to a toy piano.
If u want, send me the MIDI file and I'll save it both using General MIDI sounds and with sum quality digital sounds so u can see the difference.
phate48@fastmail.fm