I NEED HELP!!

[Brad]

I am hoping you guys can help me with this.
Here is my deal. I have this little Roland PMA-5, it is a small composer/sequencer. I have composed a piece on it that I want to turn into a midi file that I can email to this webmaster and he is going to have this midi file looping on his site. My problem is that I have no idea how to do this. The PMA-5 has a computer serial port and can be used with a mac or PC. I have a mac. What kind of software will I need, if any. Or with the serial port, will my computer just read the info as MIDI anyway? I am confused as I only have used MIDI in the controller/sound module function. Never have I dealt with actually making a MIDI file for computer audio.
I'd appreciate any help I can get.
Thanks,
Brad