Is there anyway I can do this to convert a .midi file over a duration of 1 minute long to an .mp3 format? 
Alive WMA MP3 Recorder can record your midi to MP3 format, you can download it from this website,
http://www.alivemedia.net/mp3recorder.htm
use MID Converter from http://www.midconverter.com/
With this mid converter you can convert midi to mp3, midi to wav, midi to ogg, midi to wma.
The program supports Guitar Pro files and can convert GP3 and GP4 files to audio (wav, mp3, ogg, wma) and midi formats.
The program can also convert between midi formats one into another. Supported formats are: MIDI 0, MIDI 1, RIFF MIDI 0, RIFF MIDI 1.
Why record midi? I think this is not necessary. There are programs that allow converting midi without this step, you get an mp3 file directly. A 5-minute midi file is converted to mp3 in just 10 seconds! Myself, I use Midi converter Studio, and I recommend it.
thanks